AbstractThe general objective of the research was to evaluate the performance efficiency of the Kiserian Abattoir Wastewater Treatment System. To achieve the objective physicochemical characteristics of raw influent and treated effluent from the Wastewater treatment system were determined. Samples were collected using the grab method. All samples were tested in the Environmental Health Engineering(EHE) laboratory of the University of Nairobi. The study was done in both dry and wet seasons over in a span of four weeks. Characterization of the raw abattoir wastewater revealed that most of the parameters tested had high concentrations of the pollutants. The parameters tested were COD, BOD, Alkalinity, TSS, TS, Electrical conductivity, Turbidity, Nitrates and pH. After some treatment there was appreciable reduction in the pollutants. The overall removals were COD 50%, BOD 60%, Alkalinity 89%, TSS 89%, Turbidity 65%, and Nitrates 53%. The value of Electrical conductivity increased while that of pH remained the same. Though the overall removal efficiency of the pollutants were above 50% the treated effluent failed to comply with the NEMA requirements. NEMA is a Kenyan Environment Pollution Agent((EPA). Such abattoir wastewater treatment effluent deteriorates the quality of the receiving waters. This devastates the environment and affect both human and aquatic life. Water being essential for life there is need to safe guard the quality of both surface and ground waters. There is need to improve the overall performance efficiency of the Wastewater Treatment System. The design should be modified so as to improve the performance of the abattoir wastewater treatment system. The management should liaise with the County Government to enforce pollution prevention by-laws. Regulatory bodies such as NEMA and WHO should ensure that effluents discharge from industries comply with the EPA standards.
Key words: Abattoir, Parameter, Characterization, Physicochemical, Characteristics
Livestock production is potential food for the world’s food needy people. Abattoirs are necessary units in the livestock trade providing domestic and export meat. The industry creates employment opportunities for the country’s increasing population. As the demand for meat increases the number of abattoirs also keep on increasing. The activities of cleaning the abattoirs to enhance cleanliness generates high volumes of abattoir wastewater. The generated abattoir wastewater from slaughtering area and stockyard washings comprise of blood, undigested foodstuff, animal tissue, fats and some soil from animal hooves and workers gum boots. These have the potentiality of polluting the streams (Yiu et al 2001). Effluent from the wastewater treatment system flows into the nearby streams, lakes and other surface water bodies. Such effluent should be treated to the required NEMA and WHO standards. These are the Environmental Pollution Agents(EPA) in Kenya. Untreated and poorly managed effluents are major contributor of pollutants in the receiving water CITATION Met85 l 1033 (Metcalf, 2003). Environment ends up devastated due to such discharge and causes hazardous effects on human and aquatic life. The effect may be felt either at the point of discharge or downstream. The level of pollution in the receiving water is highly affected by the number of animas slaughtered and amount of fresh water used in cleaning. Size of animals, type of the animals slaughtered and treatment processes of the wastewater treatment system also affect the degree of pollution. Excess nutrient leads to eutrophication and ends up depleting oxygen in water bodies. Aquatic life gets destroyed due to depletion of oxygen and eventually destroys the ecosystem. Other than water bodies the effluent also deteriorates environment through soil and air pollution in the alternate wet and dry seasons. Depending on the level of water table ground water may also be polluted leachet from accumulated wet solid waste. The need for good environmental safety and better health gave rise to the construction of the abattoir wastewater treatment system at Kiserian. The aim was to treat the raw influent to the required Environment Pollution Agent(EPA) standard. NEMA and WHO are environment pollution agents in Kenya. Effluents can be discharged to water bodies only if do not pollute the receiving water and create health hazards to the environment (Adelegan, 2002). Similar statement was echoed by (Metcalf and Eddy 2003). They emphasized the need for protecting both human and aquatic life. Therefore, there was need to evaluate the performance efficiency of the abattoir wastewater treatment system at Kiserian.
Kiserian abattoir is located at Kajiado County, Kenya. The Maasai who are pastoralist dominate the population of Kajiado. Animals from different areas of Kajiado and beyond get assembled at the stockyard. The stockyard acts as a market center. The animals for slaughtering are bought and directed to the slaughtering area. The area is caged so as to control the movement of the animals. Animals are made unconscious before slaughtering using a special type of gun. They are normally shot on the fore head before slaughtering. The Kajiado wastewater treatment system consists of anaerobic baffle reactor and two anaerobic lagoons. An average of two hundred and twenty animals are slaughtered. This is a summation of twenty cattle, one hundred and fifty goats and fifty sheep daily. The Abattoir wastewater treatment system uses approximately 20m3 per day. Effluent from the abattoir flows to the nearby stream which joins Kiserian River 50m away. Kiserian River water flows to Kiserian Dam which is 1.5km from the wastewater treatment system.
1.2 Problem Statement
Since water supports life it is one of the most precious resource globally. It is necessary to protect water resources from being polluted. Wastewater from abattoirs if not effectively treated may cause hazardous effects to both environment and human life. It is of paramount importance to uphold and safe guard the environment. Effluents from abattoir wastewater treatment systems should be treated to the required EPA standards. These are World Health Organization (WHO) and National Environmental Management Authority (NEMA) effluent discharge standards to surface water. Kiserian abattoir discharges wastewater to the nearby stream and eventually flows to Kiserian river and Dam. Kiserian River and Dam are 50m and 1.5km respectively from the wastewater treatment system. Since the plant is commercial buildings in town offensive smell become a nuisance to the business area. Kiserian wastewater treatment system was built to reduce the degree of pollution to receiving waters, soil and air during. Wastewater from abattoirs contain organic matter which in excess depletes oxygen in the stream and affect aquatic life and ecosystem.
Wastewater from abattoirs is amongst the toxic pollutants in receiving waters and soils. People who depend on the streams downstream for water supply, agriculture and fishing may be seriously affected by the high pollution level. Construction of Kiserian wastewater treatment system was vital as good quality water is essential for life. The aim of having the abattoir wastewater treatment system was very healthy as it meant to safe guard water quality. For such reason was need to evaluate the performance efficiency of the wastewater treatment system.
The general objective of the research is to evaluate the performance efficiency of the abattoir wastewater treatment system at Kiserian.
1.4 Specific Objectives
Determine the physicochemical characteristics of the raw influent and the treated effluent of the Abattoir wastewater treatment system at Kiserian
Use the parameters determined in (a) above to evaluate the performance efficiency of the Abattoir wastewater treatment system at Kiserian
2.1 Overview of Abattoir ActivitiesAbattoirs are points where animals are slaughtered and meat prepared either for domestic use or export. The activities of the Abattoirs seem to be sequential. Animals are assembled at the stockyard within the compound of the Abattoir for selling on the basis of willing seller willing buyer. The stockyard acts as a market area. Animals for slaughtering are caged and their movement controlled as they are directed to slaughtering chamber. Once the animals are slaughtered, blood is either collected or left to flow to the drains. The uncollected blood flows to the Abattoir wastewater treatment system. All operators in the Abattoir should be in their correct attire. These are mandatory for personal safety. After skinning, the veterinary specialist examines the meat. Splitting and washing of the entrails is done under the guidance of the veterinary officer. Cleaning of floor areas is done periodically depending on the number of animals slaughtered. Stream of wastewater and that of stockyard generates high volumes of wastewater. About 98% of the water used turn to be Abattoir wastewater. An average of two hundred and twenty (220) animals are slaughtered per day. This is a summation of twenty cattle (20), one hundred and fifty goats (150) in addition to fifty (50) sheep. Clean water used for cleaning is approximately 20m3 per day. Screens placed at intervals within the drains so as to trap the cut animal tissues during skinning so as to reduce bad smell around the abattoir area which is near commercial buildings. Trapping and removal of the animal tissues is done daily at interval of time. The undigested food is removed and stored at a shade which is later transported to convenient disposal point. The waste may also be sold for farming activities. Treated effluent from the Abattoir is then discharged to receiving water.
2.1.1 Generation of Abattoir Wastewater
Abattoir wastewater is generated from the slaughtering and washing activities. About 99% of the clean water used goes turn to be wastewater. The liquid is made of suspended and dissolved material (FAO, 1991). On the process of cleaning wide range of detergents are used and these add up chemical composition of the wastewater (Bielefeldt, 2009). Wastewater is generated at different streams within the Abattoir. The streams of wastewater include that from stockyard, animal pathways, hair removal, eviscerating, carcass washing, trimming and washing of slaughtering area (USEPA, 2004). Wastewater from the slaughtering area contains diluted blood. Blood and fats seems to be major contributors of organic matter (Nuch, 2007) and (Cowl,2001). The load reduces if blood separation processes methods are involved. Separation of blood reduces the load and the collected blood can be processed. This is the highest single water load which is eventually discharged to the receiving waters (Carawan, et al, 1979). The amount of wastewater discharged from the abattoir depends on the clean water used in cleaning activities. The pollutants noted in strong Bovine Blood as indicated by (Yiu et al. 2001) had some range limits. Total solids, BOD5 and COD were in the range of 200 000mg/L, 30 000mg/L and 300 000mg/L respectively. Untreated wastewater from Abattoirs contain high concentrations of organic matter due to the presence of fats and undigested food (Mittal, 2004). Depending on the type of feeding nitrates may be present in wastewater. Though Abattoirs are essential units in the meat industry their effluent discharge may devastate the environment. The higher percentage of Abattoir wastewater should be well managed to avoid pollution (Carawan.et al,1974). The effluent should comply with the Environment Pollution Agent (EPA) standards. These are National Environmental Management Authority(NEMA), World Health Organization (WHO). This depends on the quality of washing water used, quantity of wastewater to be treated and the volume of receiving waters. In dry seasons streams may turn to be bloody. High concentrations of Biochemical Oxygen Demand (BOD) possess a side effect as the physicochemical properties of the wastewater changes. Excess nutrients may cause deficiency of oxygen and negatively affect the ecosystem. Various approaches have been focused on treating abattoir wastewater with the objective of generating biogas. These methods included both low rate and the high rate anaerobic reactors.
2.1.2 Characteristics of Abattoir Wastewater
Characterization of the Abattoir wastewater is referenced on physical, chemical, in addition to biological composition (Metcalf and Eddy, 2003). Abattoir wastewater tend to vary widely. This is due to the type of animals slaughtered, the number of animals slaughtered, and the effectiveness of the abattoir processes (Johns, 1995), (Ittal,2004). Abattoir wastewater contain some organic matter which if not well treated to the required EPA effluent standard tend to be harmful. This may cause pollution to surface water, ground water, ecosystem and cause adverse health problems. As per (Zhan et al.2008) different rivers has determined allowable limits of accepting effluents from abattoirs as per the Table 1.
The pollution load is due to organic material in the abattoir wastewater such as blood, protein, grease and fat (Metcalf and Eddy, 2003). Pollution load reduces oxygen in receiving water and cause suffocation to living organisms (USEPA, 2009). Depending on the volume of receiving water the turbidity rises and appear bloody. This reduce the aesthetic value of the receiving water. The characteristics of the receiving water is highly influenced by the characteristics of the treated abattoir effluent. The values of the characteristics of generated abattoir wastewater should be compared with the EPA values so as to determine their pollution level to receiving water. Pollutants concentrations as per the table of (yiu et al. 2001) shows a concentration range as provided in table 2.
Abattoir wastewater characterization is pegged on physicochemical and biological composition. Characterization is essential as the findings serves as a tool in design of a wastewater treatment system. Results also assist modification in treatment process and enable the selection of most the economical treatment processes. Decisions made on the basis of the results enables the designer to plan for more effective wastewater treatment system (Metcalf and Eddy, 2003). Abattoir effluent contains organic matter and high content of BOD and COD (Kobya et al, 2005). The quality of abattoir wastewater depends on the effectiveness of the treatment method, blood present in the effluent and the type of animals slaughtered (Masse and Masse 2000). Values of undiluted blood for COD and BOD5 range as 300,000mg/L and 30, 000mg/L respectively (Yiu et, al. 2001). As per (Yiu et, al 2001) the value of Total Solids was 200, 000mg/L. In a wastewater treatment system, the values may be reduced by modifying the treatment method. Abattoir wastewater must be treated effectively to avoid deteriorating the environment. Such high levels cause eutrophication, loss of aquatic life and pollution of receiving water. Treated effluent from the treatment system should be tested on routine basis (Metcalf and Eddy, 2003). The data recorded over a period of time becomes useful in design of abattoir wastewater treatment systems and for modifying un performing existing system existing system.
2.1.3 Impacts of abattoir effluent to environmentIn most cases Abattoir effluent have negative impacts to built-up environment, residents around the abattoir, soil and water(FAO,2009). Abattoir wastewater contains both insoluble and suspended biodegradable material whose rate of breaking down is very low (Sayed et al. 1088). The presence of large quantities of suspended matter lessens light penetration of sunlight into water bodies (USEPA, 2002). Effluent from abattoirs contain nutrients such as Phosphorus(P) and Nitrogen(N). These causes eutrophication. Reduction of oxygen content in the receiving water and negatively affect aquatic life (USEPA,2002) as it suffocates the living organisms. Untreated effluent pollutes water sources and cause adverse health hazards to human life. Since water is essential for human it should be protected from pollution (USEPA,2002). Untreated effluent reduces the fertility of soil as the pores of the soil gets clogged and prevent effective aeration. This may result to poor harvest and cause famine. Atmospheric condition may be affected due to bad smell from the untreated effluent (Metcalf and Eddy, 2003). The Abattoir influent should be treated satisfactorily as per EPA standards. This will result to better environment and reduce water borne diseases.
2.1.4 Guideline principles of treating abattoir wastewater
The systems of treating wastewater are carefully designed so as to remove harmful contaminants which may be hazardous to human life and the environment. The reduction of the contaminants to acceptable levels will eliminate the risk of polluting the receiving water and safe guard human health, aquatic life and the environment (McKinney, 2004). Adhering to the required EPA standard will allow the discharge of industrial liquid wastewater without the risk of polluting the natural environment (FAO 1992). The guiding principles of treating wastewater may be enlisted as preliminary that removes large objects, primary treatment that removes floating material. Coagulants may be used to accelerate the process of sedimentation and flocculation. In secondary stage biological and chemical process appear effective. Tertiary treatment may be applied as a polishing process but may be not necessary.
Biodegradable material may be brought to acceptable standards by either aerobic or anaerobic processes. A ratio of BOD: COD of < 0.5 shows that the organic matter is biodegradable (Metcalf and Eddy) these values should be determined before designing the treatment system. These processes use bacteria and seem to be effective. The bio gradable material can be acted in aeration tanks, facultative tanks or lagoons or membrane filters (Metcalf and Eddy, 2003). Various approaches have been used in treating Abattoir wastewater focusing on sewage treatment and generation of biogas. These methods included the low and high rate reactors. The low rate systems may not cope with the higher volumes of abattoir wastewater hence the two types of reactors are integrated for faster and effective process (Metcalf and Eddy).
2.1.5 Physicochemical treatment
Wastewater from abattoirs is made to undergo primary treatment units. In these units it is made to pass through the process of screening to remove the bigger solids and then through the catch basins followed by flow equalization (USEPA,2008). Suspended solids and the very small colloidal materials and fats are removed from the wastewater. The diffused air method (DAF) is also used to inject air bubbles from the bottom. This removes the very light particle and hydrophobic material. AS the process is on grease and fats are brought at the top and the suspended scum skimmed off (Camin,1970). Flocculants are normally added to accelerate the flocculation process for better performance (USEPA, 2008). Nutrient can also be removed by using physicochemical method.
2.1.6 Biological treatment
Industrial wastewater may also be treated by using biological treatment methods. This method removes organic matter. Inorganic compounds and pathogens are also removed from wastewater (Metcalf and Eddy, 2003). The method can get rid of 90% pollutants from the industry wastewater (USEPA, 2002). Aerobic and anaerobic processes remove total suspended solids from wastewater if there is the required contact time with the microorganism. The method can be used in combination of anaerobic pods and facultative lagoons (USEPA, 2008). Biological processes are flexible and are used in physicochemical processes. The method appears more effective and economical. The main biological processes include the facultative and anaerobic processes which operate in absence of oxygen unlike aerobic which require oxygen. The BOD and cod ratios of the raw wastewater should not exceed 0.5. If within the ratios then the abattoir wastewater is biodegradable (Metcalf and Eddy, 2003). This remain to be a guide in biological processes of organic matter. The plants which use biological methods can easily be redesigned and modified to suit the situation. The method seems to be working in many wastewater treatment systems.
2.1.7 Aerobic treatment
Aerobic processes need oxygen for effective operations. Oxygen may either be supplied from the atmosphere of by air diffusion. Air diffusion mostly operate by using electricity. This turns aerobic process to be uneconomical. Carbonaceous BOD5 is effectively removed by an aerated process. By oxidation suspended material are also removed. Aerobic treatment is also used in domestic wastewater treatment. Treatment units as biological filters, activated sludge process and either shallow ponds or aerated lagoons commonly use the aerated process. The process results to large quantities of sludge. Removal of such high amounts of sludge and the use of power increases the operation cost (Metcalf and Eddy, 2003). The method is mostly used in meat industries (Yiu et, al., 2001). This method appears effective in wastewater treatment. Air diffusion create air bubbles in the treatment. This creates turbulence in the liquid. The mix become flocculent and the colloidal material become homogeneously mixed. These are made to settle and removed as sludge (Metcalf and Eddy, 2003). The clear liquid is passed through shallow ponds or lagoons and the remaining small particle are acted upon by aerobic bacteria using oxygen from the atmosphere. The large quantities of sludge produced by activated sludge process can have monetary gain once sold for agribusiness activities.
2.1.8 Anaerobic digestion
Anaerobic digestion is a fermentation process where organic material gets degraded and generate biogas, mainly methane and carbon dioxide produced (Palprasert 1989). Anaerobic digestion occurs in many activities so long as there is organic material and low redox potential (nil oxygen). In numerous developed countries, the process has been engaged with the purpose of bio-stabilization of the fermentable biodegradable waste generated in urban and rural area undertakings (Van Lier et al. 2001). Anaerobic digestion is not suitable in cold climates. The detention period is between 20-50 days. Biological stabilization of organic materials involves hydrolysis and methanogenesis bacteria activities (Siegrist et al., 1993). Anaerobic processes are economical as they operate in absence of oxygen. It does not require electricity for air diffusion. The system is convenient for small-scale wastewater treatment system. It is best suited for rural areas where large areas of land are available (Metcalf and Eddy 2003). The design should provide long length so as to have longer time of bacteria activities. The retention time of the influent to effluent is between 5 days to 15 days. Depth vary from 3m and 6m. The initial stages of anaerobic processes may require incubation. The transfer of bacteria from existing Waste water treatment plants. This accelerates the process the bacterial process. The principal processes in anaerobic digestion include acetogenesis, hydrolysis and methanogenesis which eventually ends up with the acidogenesis process (Siegrist et al., 1993). These are as outlined in figure 3.
2.1.9 Operating temperatures in anaerobic digestion
Anaerobic digestion as in facultative processes operate in certain range of temperatures. Some anaerobic reactors function at either mesophilic or thermophilic degrees with an optimuma of 35oC and 55oC, correspondingly (Gujer & Zehnder,1983). Microbial bacteria or organisms’ communities behave differently at optimal temperatures. Changes from mesophilic temperature to thermophilic temperatures result in decrease in the production of biogas. This may only change when the population of the organisms’ increase. Slight temperature changes from 35oC to 30oC and from 30oC to 32oC have been demonstrated to lessen the rate of biogas production. As per Ganoun et al., 2007) observation anaerobic digestion of pooled abattoir wastewater and olive mill at 35oC and 55oC thermophilic anaerobic reactor yield a higher biogas and COD removal than mesophilic anaerobic reactor. High activity levels of organic rate generally sustain high yields biogas production.
In the innitial stage the activites of the anaerobic activities may not pick up at ahigh rate. The process can be accelerated by seeding with existing sludge. This is merely the carrying of organisms which are already active to activate the process. Generation of the biogas will give a proof of an operating process. Ruminant manure seeding is also effective and can lessen starter-up time. Wash out of the microorganisms is normally reduced by introduction of organic matter at a low rate. (Huand Yu, 2005).
Maximizing seeding is expected to provide a constant output of biogas in stabilization phase (Martin et al., (Martin et al.,2003) suggested that reactions transpire in certain agitated interface amongst depleted and the raw wastes matter as the boundary of the depended micro-sites in the anaerobic reactor (Martin, 2001).
After the assembling, the retention time in which the sludge is left within the receptacle is dependable on the temperate and vary from considerably. At the optimal temperatures, of 20oC to 30oC daily mean is required as reported by FAO, 1996). Temperature fluctuation needs to be minimum as applicable because of microorganisms’ temperature sensitivity (ISAT/GTZ, 1999). If biomass temperature is below 15oC, then the production of gas is low in the plant. At high temperatures the production of methane will increase (ISAT/GTZ, 1999).
Anaerobic reactors perform better if some mixing is effected so as to keep the material on agitated (Burton, 2003). In a basic anaerobic reactor, the contents of most anaerobic digesters are mixed to ensure efficient transfer of organic material for the active microbial biomass. Mixing will prevent sedimentation of denser particulate material. Mixing is normally done at intervals. This depends on the type of anaerobic reactor, the agitation done and the total solids value of the feedstock.
There different methods of mixing. They vary greatly as mentioned by (Karim et al., 2005). To mix the material within the reactor propellers can be used if the feedstock is of a suitable low viscosity. Some pilot scale reactors have used a screw in a central tube to give downwards movement and some European manure digesters used a similar principle to give upward movement from propeller located at the bottom of the digester, through a central draught tube. To prevent the need of moving parts within the reactor, the recirculation of biogas through the bottom of the reactor or hydraulic mixing by recirculation of the substrate with a pump can be used to achieve adequate mixing. For the case of the study, mixing will ensure active process hence effective results in reducing levels of pollution of the effluent. Analysis of Abattoir wastewater is essential in determining the level of pollution (Hammer, 1990). Abattoir wastewater are suited for anaerobic treatment if they have high organic matter, sufficient organic biological nutrients, and free toxic materials. Anaerobic lagoons are also used to treat abattoir wastewater. It can also be done by combining it with anaerobic baffle reactor (Anders et al., 1968).
2.2.1 pH Values
Anaerobic digestion operates well under a pH range of 6.8-7.2. The rate of growth is methanogens and is notably reduced (mosey ; Fernandes, 1989). At higher alkaline pH levels there is the disintegration of the microbial granules leading to subsequent botch of the process (Sandberg,1982). A pH of 7 is the optimal methagenesis, pH range of 5.5 to 6.5 has been reported to be the optimal hydrolysis pH (Kim et al., 2003). Due to this some designs separates methanogenesis/acetogenesis and the acidification/hydrolysis processes to a two-stage process.
In aerobic fermentation, buffers capacity in most cases is referred to as alkalinity and is the steadiness of CO2 and the bicarbonate ions which provide resistance to the significant and the rapid pH variations and therefore buffering capacity is proportionate to bicarbonate concentration. According to Guwy et al., (1997), it is more reliable to measure digester imbalance with buffer capacity than the direct measurement of the pH as the fatty acid accumulation will lessen the buffering capacity significantly before the decreases in pH. Low rate of organic loading best accomplishes the increase of the buffer capacity Under these conditions, digesters can be used to check the pollution level and optimize the efficiency of the abattoir treatment system. It is always necessary to monitor the parameter of the system closely to obtain good results.
According to Pullammalanappallil et al., (1998) several anaerobic digesters contain adjustable feedstock sources that may cause the chemical fluctuations in the reactor composition. Due to poor monitoring structures, most anaerobic digesters are currently run at a lower than the optimum rate of loading to prevent the occurrence of instability within the digester. Often, the instability results from the inhibition of the methanogens by the surplus fatty acids. Therefore, it is of utmost significance to maintain an equilibrium between the fatty acids and the system’s buffering capacity. During the study, samples will be taken at short intervals for better observation. Adherence to the results of the analysis will reduce generation greenhouse gas emissions from fro abattoirs that result from methane (CH4) emissions from untreated organic waste and wastewater.
Digesters with High efficiency permit a high degradation rate with little input of energy and simultaneous production of biogas (with the average of CH4- content of 60-75%). As the objective of the study is the performance of the system, high biogas production will indicate and efficient treatment. According to reports obtained from Technical information W5e gtz (http://www.gtz.de/gate/gateid.afp), the loading rate for the digester ought to be lower than 3kg COD/m3 digester per day leading to a 0.67m3/m3 digester volume of waste water daily with an average 2,000mg COD/I pollution load. Systems that are suitable reduce the COD by about 60% to 75%. The general effectiveness and the wastewater treatment efficiency will be increased by the facilities for the effective primary mechanical treatment prior to the secondary steps of treatment. More importantly, the physical removal of solids, fats are more economical than any other elaborate application of the tertiary and secondary treatment steps.
2.2.2 Low Speed Reactors
Anaerobic lagoons are classified as low level reactors. Wastewater from abattoirs can be treated by anaerobic lagoons under the process of anaerobic digestion. However, the rate of digestion low. Depending on the volumes of the abattoir effluent sizes of anaerobic lagoons may vary from one abattoir to another. The designs are simple and economical making them viable in many areas. Their depth varies from 3.5 m to 6 m. There should be a difference in levels. This will create the gradient for the flow. Depending with the number to be used the arrangement should be in series or parallel. Anaerobic lagoons require bigger area of land which may not be available in urban setting. The unpleasant smell makes them not environment friendly (Metcalf & Eddy, 2003) especially abattoirs neighboring commercial building. However, they may be used with anaerobic baffle reactors to accelerate the rate of digestion.
2.2.3 High Speed Reactors
Basically there two types of anaerobic reactors. The high rate(action) and low rate reactors. The high rate has a faster action. Hulshof & Lettinga (1986) suggest that all contemporary fast biomethanation procedures reflect the conception of withholding high workable biomass by immobilizing the sludge developed by the anaerobic bacteria. The high rate reactors include, Anaerobic Sequence Batch Reactor, Anaerobic(ASBR), Anaerobic Fluidised Bed Reactor(AFBR), Up flow Anaerobic Sludge Blanket Reactor and Anaerobic Baffle Reactor(ABR). The high rate reactor acn be used separately or combined with the low rate reactor (Sayed. S.K. I.,1987). The decision is controlled by the concentration of the pollutants.
2.2.4 Anaerobic Sequence Batch Reactor (ASBR)
The anaerobic procedure would be attractive to the abattoir wastewater treatment industry. The anaerobic sequencing batch reactor has the prospect of being a low-cost venture as well as being an efficient system to eliminate the suspended solids and soluble COD. The process might also eradicate the necessity for the air flotation and the sedimentation processes that is currently used at some abattoirs. The cost effective technology in operating and maintenance makes it an attractive process (Sung & Dague, 1995). Studies by Massé & Masse (2000) have indicated that (ASBR) have produced excellent results in treating abattoir wastewater. From most studies, it is evident that higher biogas generation is indicative of effective treatment. The ASBR represent a fairly modern anaerobic system that is of high-rate. In this system there are four treatment stages These stages are sequential processes as illustrated in figure 4. This type of reactor is effective in high strength wastewater. The average detention time range from 8 to 24 hours. It removes up to over 75% COD. The biomass seems to have more than one type of bacteria. The granules have a high rate of settling. The system is still under observation (Masse’ and Masse, 2000). The sequential processes depend on the timing intervals.
At both the feed and react stages, the reactor is mixed to facilitate the local connection between organics and bacteria. The manner of mixing must be extremely mild to avoid disturbing bacterial flocs from forming. Sporadic mixing is an alternative to constant mixing since it increases biomass sedimentation and reactor efficiency (Sung and Dague, 1995). The food to microorganism (F/M) quotient is steep at the start of the reaction stage and consequently, organic transformation into biogas, according to Monod kinetics, is at its peak (Sung and Dague 1995). The duration of the reaction will be contingent on substrate features and waste quality necessities.
For effluents containing great SS concentrations, more interaction time between substrate and bacteria is mandatory for all the particulates to hydrolyze. Once the rate at which gas is produced has attained a minimum value, the content of the reactor is set to settle. The low F/M ratio when the reaction stage terminates helps biomass flocculation and sedimentation (Sung and Dague 1995). As the biomass settles, the CO2 partial pressure over the liquid region remains the same and in balance with dissolved CO2. Thus, no substantial magnitude of CO 2 is relocated to the headspace, therefore contributing to the creation of tranquil setting environments.
As soon as the biomass turns into a solid layer at the foot of the reactor, the supernatant is drained at a predetermined level, usually at an expanse above the biomass bed. As the waste drains, microorganisms which don’t settle easily are also detached from the reactor, deserting the denser bacterial flocs (Sung and Dague 1995).
2.2.5 Anaerobic Fluidized Bed Reactor (AFBR)
Perez et al. explain that here, the platform for bacteria to connect, grow and develop is sustained by a fluidized form of tug forces stemming from the streaming liquid effluent (1998). The platforms utilized are activated carbon, minute particle size sand, among others. In liquid form, all materials offer an expansive surface area for the creation and development of the biofilm. It permits the high reactor plant and animal waste to be held-up and additionally stimulates the whole process to be not only efficient but also steady. This results in an opening for a greater placement of biodegradable matter and superior opposition to sources that slow down the process. Fluidized bed technology is more efficient compared to other technologies as it promotes microbial cells to be transmitted from the dense solid and liquid mixture to the brim and therefore augments the microorganism-substrate interaction.
2.2.6 Up-flow Anaerobic Sludge Blanket Reactor (UASBR)
The UASB is an innovation tool that is currently utilized broadly to treat wastes from different emission agents notably, food processing entities, municipal wastewater, distilleries, tanneries, etc. The dynamic plant and animal waste represented as dense solid and liquid granules is stored in the reactor. UASB is cost efficient since it uses minimal pump energy for recirculation of wastewater (Rajeshwari et al., 2000; Lettinga & Hulshoff 1991; Wentzel et al., 1995). Among prominent drawbacks, is that it takes an extended period of time to start, and it also demands an adequate quantity of granular seed sludge to catalyze the start-up.
2.2.7 Anaerobic Baffle Reactor (ABR)
Over a period of time wastewater has been treated by using both aerobic and anaerobic processes. Aerobic lagoons have shallow depth and oxygen may be obtained from the atmosphere or by diffusion process. Aerobic process appears to be more expensive as more energy is required to agitate the supply of oxygen. It produces high volumes of sludge and this may require intense labour hence not economical. Anaerobic processes do not require supply of oxygen. The organism can do without oxygen. Anaerobic baffle reactors can be improved and septic tanks and are high rate reactors. They are better option of treating abattoir wastewater (McCarthy,1985). The mode of construction of anaerobic baffle reactor allows movement of bacteria and create a gentle interaction with the high quality of each biomass. The process is well effected by the up and down movement within the compartment of the anaerobic reactor (Grobiki & Stkey,1991). Anaerobic baffle reactors are very significant due to their ability to segregating acidogenesis and methanogenesis as the flow of wastewater moves from one stage to another within the compartments.
This is attributed to the fact that various states emerge at various points during breakdown relating to pH, substrate concentration, and temperature. Different regions bring about the establishment of findings in assorted microbial populations that are modified by the prevailing surroundings specifically, acidogenesis in the beginning and methanogenesis at the culmination. As such, bacteria develop under the most desirable environment demarcated by the temperature and the pH. Due to the high volumes of wastewater and the ability of the high rate treatment, the system is highly suite for large scale operations (Orozco, 1997). This can be achieved by the fact that the reactor can function without electric power as effluent can be directed to the reactor through the force of gravity (Foxonet al., 2004).
Anaerobic baffle reactor has upright baffles which force the wastewater move up and down the compartments. The movement allows homogenous mixing as the active biomass on its movement within the compartment of the anaerobic baffle reactor (Barber, 1999). There are different groups of organism acting in the anaerobic baffle reactor. These are the acidogenic, acetogenic and the methanogenic.
The anaerobic baffle reactor maximizes the interaction between the biomass and the effluent composed of dissolved and floating materials. Improvements on anaerobic baffle reactors was developed and various alterations have been implemented to boost the reactor performance. The driving force behind these adjustments is that it has to enrich the solid preservation capacity. Design amendments were made so as to have a more efficient system of treating abattoir wastewater.
Anaerobic digestion that occurs in an Anaerobic Baffle Reactor consists of various sets of organisms. The ranging from the hydrolytic fermentation (acidogenic) bacteria which perform the hydrolysis process to convert the composite polymer substrate to alcohol, hydrogen, sugars, organic acids, and carbon dioxide. Secondly, the hydrogen generating acetogenic creatures that transform fermentation products of the former hydrolysis and acetogenesis phase into carbon dioxide and acetate. Third is the methanogens that facilitate the conversion of simple compounds notably methanol, acetic acid, hydrogen and carbon dioxide to methane. It observable again that the quadruple-step process that usually regulates the organisms’ response in an anaerobic process are: hydrolysis, acidogenesis, acetogenesis, and methanogenesis respectively. As a result of these processes, biogas is generated.
3.0 MATERIALS AND METHODS
3.1 Sampling of Raw Abattoir Wastewater and Treated EffluentGeneration of the abattoir wastewater is as a result of the abattoir activities. These include slaughtering and washing of the floor area where there is a lot of blood. The Kiserian abattoir does not have blood separation facilities. Most of the uncollected blood flows the drains and eventually to the wastewater treatment system. This makes the treatment of the raw abattoir influent complex. Cuttings are trapped by the screens placed at intervals within the wastewater treatment drain. Almost all the clean water used in washings turn to be the abattoir wastewater. Some samples of the untreated abattoir wastewater and treated effluent from the wastewater treatment system were collected for testing. All samples were collected and tested in the Environmental Health Engineering laboratory of the University of Nairobi. Samples for testing were collected at specified points within the wastewater treatment system drain using grab sampling method. Collection of samples was done in wet and dry seasons. The raw wastewater samples were collected at three points within the drain conveying raw abattoir wastewater. The first samples were collected just after the first screen. This is a point where there was some agitation of the flow due to some turbulence. The agitation enabled the collection of homogeneous samples was designated as P1. The second point was designated as P2. This was a midpoint of P1 and the entry to the treatment system. The third point was designated as P3. This point was at the outlet of the abattoir wastewater treatment system before the effluent joined the stream. A total of 24 samples were collected. 12 samples during the dry season and the other 12 samples during the wet season. The Abattoir treated effluent samples were collected immediately at the outlet of the wastewater treatment system before it joined the nearest stream. The Kiserian abattoir wastewater treatment system was 80 m from the Kiserian River and 1.5 km from the Kiserian Dam. Sampling was done between 8.00 am and 10.00 am. The timing reflected peak activities of the abattoir. at two weeks’ interval. Collected samples were taken to the laboratory to determine the concentrations of the pollutants in the parameters. The parameters determined during the study were: COD, BOD5, Alkalinity, TSS, TS, Electric conductivity, Turbidity, Nitrate and pH. Collected samples were transported in plastic bottles to the laboratory. All the bottles used were well cleaned and rinsed with de- ionized detergents. Samples for BOD and COD were carried in BOD bottles and for COD in plastic bottles wrapped in aluminum foil. All samples were preserved at 4oC and tested in the Environmental Health Engineering laboratory at the University of Nairobi.
3.2 Abattoir Wastewater CharacteristicsCharacterization of the abattoir wastewater was done in a laboratory using different methods as outlined. Tests were done on both the abattoir raw wastewater and the treated effluent. Tests for each parameter were done in the Environmental Health Engineering laboratory. Chemical oxygen demand (COD), Five days’ Biochemical oxygen demand(BOD5), Alkalinity, Total Suspended Solids(TSS), Total Solids (TS), Electric conductivity(EC), Turbidity, Nitrates and pH. were determined in each of the collected samples. For the COD test Reflux apparatus with Erlenmeyer flask with ground glass joint, Glass beads and Pipettes were used. The test measures the amount of organic compounds in the abattoir wastewater sample. It is an important test as it has great effect on the quality of receiving water. BOD is the amount of oxygen required by the aerobic biological organisms in wastewater. This activity occurs when the bacteria are feeding on the organic materials present in the samples. Higher levels of BOD indicate higher pollutions and contaminants in wastewater. BOD levels assist in designing wastewaters treatment systems. The parameter was determined by incubating the samples in the dark for five days. Some two dilutions were prepared so as to get the correct BOD values. In this case Incubator, DO meter, Burettes, Pipettes and Beakers were used. Electrical conductivity is the ability of the abattoir wastewater to conduct some electric current. This signifies the presence of dissolved ions in the abattoir wastewater. It was determined by using Conductivity meter. The pH of the samples was determined by using pH meter and a beaker. It determined acidity and alkalinity of the abattoir wastewater. Suspended solids were determined by using Vacuum Pump, Oven and Filter Paper while total solids of the samples were determined by using Water bath and Evaporating dish. Nitrates of the Abattoir wastewater were done by using Lovibond comparator, test tubes and pipettes. Alkalinity enables to gauge the ability abattoir wastewater in accepting protons. This is to neutralize acids. Alkalinity was determined by titration using burettes, pipettes and Erlenmeyer flask. These tests were conducted on each of the samples collected and the results tabulated in the tables provided. The turbidity of the samples was done by using turbid meter after making the suspensions. Turbidity is due to the colloidal material which remain suspended in water. It is not pleasant and can be harmful. The colloidal suspension may be caused by silt, microorganisms and sewage due to intrusions from sewers.
3.3 Laboratory Tests Procedures Conducted on Abattoir Samples3.3.1 Chemical Oxygen Demand (COD) TestThis is a gauge of the amount of oxygen needed to oxidize the organic material in the collected samples. This happens in specified controlled oxidizing agent, controlled temperature in a given time. The test is essential as can reflect the toxic conditions in the samples. The Organic material which tend to be resistant to biological treatment may be identified. The reagents used distilled water, standard ferrous Ammonium Sulphate (0.025N), ferric indicator solution, powdered Mercuric Sulphate and Sulphuric acid. The apparatus used for the test were the refluxing apparatus, Erlenmeyer flask with ground glass joints, glass beads and pipettes. Refluxing was done for 3 hours. The results obtained for all the samples were tabulated as entailed.
3.3.2 Biochemical Oxygen Demand (BOD)
The apparatus used for the test were incubator, DO meter, burette, pipettes and beakers. After making the dilutions the samples were incubated at 20oC for 5 days. This was by using the Wrinkler method. The reagents were starch indicator solution, concentrated Sulphuric acid, Magnesium Sulphate solution and thiosulphate solution. The reagents for water dilution were Phosphate buffer solution, Ferric Chloride solution, Calcium Chloride solution and Magnesium Sulphate solution. The results of the 5 days’ incubation were tabulated in the tables. The tables provide the 5days BOD for all the samples.
3.3.3 Total Solids (TS)
Solids can either be in organic form or inorganic form. In wastewater solids may be suspended or in solution. The weights of the evaporating dishes were determined after oven drying and cooling, and then stored in a dedicator to maintain the temperature. Sample was then dried by evaporation at 103oC. The Total Solids concentrations were tabulated for all samples.
4.0 RESULTS AND DISCUSSIONSThe assessment of the concentrations of the treated abattoir wastewater was essential as it affects the quality of the receiving water and environment. The tests conducted on the influent and effluent determined the concentrations of the pollutants. The results enabled the evaluation of the performance efficiency of the treatment system. Designing of an effective Abattoir treatment unit particulars is pegged on such results. Abattoir treated effluent must comply with the required standards of the environment protection agencies(EPA). These are NEMA and WHO. Adherence to the allowable standards is of paramount importance as clean water is essential for life. Water resources should be well protected and managed. Water related diseases will be kept at bay. This will lead to good health and productive nation. The parameters tested were COD, BOD, TS, TSS, Electrical conductivity, Nitrates, Turbidity, Alkalinity and pH. Discussions on evaluating the performance efficiency were developed from the results obtained in the laboratory tests and analysis.
Table 8 provides results on the tested parameters in dry and wet seasons. It was evident that there were variations in the characteristics of the parameters in both seasons. For the dry and wet seasons, the pH mean values were 7.2 and 7.89 respectively. These variations were not so high. The values of the pH were within the allowable range of the NEMA standards. NEMA standards for discharging to surface water being 5 to 9. Electrical conductivity of the Abattoir effluent in the dry and wet seasons were 9485 ?Scm-1 and 10900 ?Scm-1 respectively. The increase in the ions could be due to dissolution of cattle deep remain on the animal’s skin during slaughtering. Animals were not washed at the cage before slaughtering. Salts from the nearby hides preservation rooms within the compound could have leaked to the Abattoir drains and contributed to the increase of ions.
The values of Table 9 and those of Table 2 differ. The concentrations of the raw influent are relatively higher. These values do not comply with the NEMA allowable limits for discharging abattoir wastewater to surface water bodies. The raw influent should be treated to the required (EPA) standards.
4.1 Evaluation of the Abattoir Wastewater Treatment System
The performance of the Abattoir wastewater treatment system was based on the level of pollutants removed from the samples of Abattoir wastewater which entered into the treatment system. The pollutants of the raw influent samples and those of the treated effluent samples were determined. This was done in the Environmental Health Engineering laboratory at the University of Nairobi. The difference in the values of raw influent samples and those of treated effluents samples values were determined. The Evaluation performance efficiency of the abattoir wastewater treatment system was based on the variations of the values as obtained in Table 10. The mean values of raw influent and treated effluent were used in calculating the removal efficiency.
Removal efficiency of the system:
The concentrations of the pollutants in each parameter tend to vary at each sampling point. The concentrations appear to be variable as they are functions of the abattoir processes and season of the year (Mittal, 2006). Some particular cases reveal clear variations at peak points. This could be due to the variations of the number of animals received and slaughtered at different times of the season. Initially the raw wastewater which entered into the Abattoir appeared bloody and not aesthetic. The turbidity was high, at 37(JTU). All the parameters tested had high concentrations of pollutants. COD, BOD, TS, TSS, Electrical conductivity, and Nitrates (Table 10).
After the treatment process the characteristics values of the treated effluent changed. This was due to the reduction of the pollutants concentrations. There was appreciable removal of pollutants (Table 10). The overall removal was above 50% in each tested parameter. The effluent became clearer than the influent. The offensive smell reduced and the surrounding area became attractive for business as the area is surrounded by commercial buildings.
The mean values were obtained from the 12 samples of abattoir wastewater. The mean values provided the main data for the research. There were variations in each of the parameter. The variations could have been due to the different types of animals slaughtered and the quantity of the animals. The mean values provided the working figures in decision making. The values help in design and modification of the treatment system.
The reduction of the pollutants in each parameter was almost 50%. This shows a high reduction of the pollutants. Though the reduction was high the overall reduction did not meet the allowable NEMA standards. There is need for some modifications in the system. Increasing the length of the ABR and adding an extra lagoon would increase the performance efficiency removing the pollutants.
The overall removal of the organic load was as indicated in Table 9. The results revealed that overall removal efficiency of pollutants was appreciable high though the levels did not meet the EPA standards. The removal of pollutants in COD was 50%, that of BOD 60% and 89%. The removal of the organic load was distinct but relatively lower to the NEMA requirement. Some corrections should be done so as to meet the required standard. The operations and maintenance team needs to be more vigilant in repairs. The length of the ABR should be increased so as to detain the abattoir wastewater much longer. The design should not encourage overflows.
The overall performance efficiency removal of TSS, TS, and Turbidity were 89%, 66% and 65% respectively. The removal of TSS was notably high. Due to such removals the effluent was clearer relative to the influent as per Table 4.1. However, more traps should be installed within the channel. That will have increased the trapping of material. There should be provisions for getting rid of soils and preventing it flowing to the abattoir wastewater treatment system.
The removal of nitrates was averagely high. The depth of the lagoons do not provide free dissolved oxygen. The denitrifying bacteria at such depth use the organic matter as electron donor. This depends on several factors as temperature and pH. For the TSS the overall removal is 89%. This is significantly high as per Table 9. The abattoir wastewater treatment system for this pollutant was satisfactory.
From Table 10 it was evident that there were variations in the characteristics of the parameters. For the dry and wet seasons, the pH mean values were 7.2 and 7.89 respectively. The variations were not so high. The values of the pH were within the allowable NEMA standards. The required NEMA standards to surface water being 5 to 9. The Electrical conductivity of the Abattoir treated effluent in the dry and wet seasons were 9485. ?Scm-1 and 10900. ?Scm-1 respectively. The increase could be due to dissolution of salts in the nearby hides preservation compartment within the compound.
The pollutants of the influent during dry and wet seasons tend to differ as per Table 10. From the records more animals were slaughtered during dry seasons than wet season. Type of animals and the type of feeds in the two seasons could have contributed to the difference in pollutants. Electrical conductivity increased during wet season. Some salts from the nearby hide preservation room may have found way to the drains. Washing from Agricultural land may have been washed to the drains. Infiltrations from surface water may have passed through the poorly maintained drains of the wastewater treatment system.
Performance of the Abattoir Wastewater Treatment System at KiserianAfter testing the raw and treated effluent the analysis of the physicochemical and biological indicated some differences. The characterization of the parameters revealed some changes in the pollutants level. The objectives of the research were to determine the characteristics of the raw influent and the treated effluent. The values of the characterization were to be used in determining the pollution load and evaluate the overall performance efficiency of the abattoir wastewater treatment system. Collection, testing and analyzing of the samples were done between the months of ………………….and ……………………………..
The level of pollutants in each of the three sampling points showed some differences. Variations in the characteristics was very vivid in COD, TS, TSS. and Electrical conductivity. The number of animals slaughtered per day varied. In some seasons the demand for meat was high hence more animals were slaughtered. That could have caused the variations of the distinct characteristics differences of the raw wastewater in the tested samples. The percentage removal of the pollutants seems to be high as shown in Table4.2 The values recorded indicate appreciable removal of the pollutants.
Comparison of the Effluent Values with the NEMA Allowable Limits
The overall percentage removal of pollutants appeared high in the beginning. However, the values were not complying to the maximum allowable NEMA discharge limits to surface water. All Abattoir wastewater treatment systems should comply to the environment pollution agent(EPA) requirements. Failure of which leads to pollution to the receiving water. That would cause health hazards to human life and devastate the environment.
CHAPTER FIVE5.0 Conclusions and Recommendations5.1 Conclusions
The characterization of raw abattoir influent and treated effluent provided useful data in evaluating the performance efficiency of the abattoir wastewater treatment system. The raw abattoir wastewater was found to have high concentrations of pollutants of COD, BOD, TSS, TS, Electrical conductivity and Alkalinity. There were some variations of pollutants of the parameters of the samples tested. Apart from pH, Alkalinity and Nitrates all other parameters tested were high. That could have been contributed by the number of animals slaughtered per day. The type of animals slaughtered could also affected the difference in the concentration of pollutants in the parameters. Other factors which could have affected include the amount of water used in the different streams, the type of animals feeds used and the mode of separating rumen content. The high concentrations of the pollutants affect the quality of the receiving water. This would devastate the environment and cause health hazards. After the treatment the results were encouraging as there was appreciable reduction of the pollutants as per Table4.2. However, the overall performance of the wastewater treatment system did not comply with the allowable NEMA standards. Good environment means better health. It is mandatory to improve the abattoir wastewater treatment system. This will optimize the efficiency of removing the pollutants and safe guard the quality of the receiving water. From the results of the research, the performance of the abattoir wastewater treatment system at Kiserian is below the NEMA allowable standards. There is need to make arrangements of improving the performance of the abattoir wastewater treatment system to meet the required NEMA standards.
From the study the following points are recommendation for the abattoir wastewater treatment system at Kiserian.
The Abattoir wastewater management team should keep daily records of the characteristic of the raw influent and treated effluent for analysis
A high rate anaerobic reactor should be incorporated within the existing abattoir wastewater treatment system.
Management should keep records of the amount of water used on daily activities, the number of animals slaughtered and the type of animals for spot checks
The County Government should enforce by-laws and oversee the activities of the Environment Pollution Agent (EPA)
Abattoirs should have small laboratories to test and analyze the abattoir wastewater generated by the treatment system
Defaulters of the by- laws should be sued in a court law
Abattoir management should support research work so as to develop new technologies in abattoir wastewater treatment
Abattoir operation and maintenance team should be inducting new employees for better workmanship
Managers should benchmark with other abattoir Wastewater treatment systems which comply with the NEMA and WHO standards. This will lead to higher performance.
The upcoming of car washing activities should not be allowed near Abattoirs
The demand for meat keeps on increasing due to the rise in population. It should be mandatory to register all operating abattoirs in the area.