MESOCOSM STUDY ON THE POTENTIAL USE OF VERTICAL SUB-SURFACE FLOW CONSTRUCTED WETLANDS FOR REMOVAL OF ORGANIC MATTER IN SLAUGHTERHOUSE WASTEWATER

ABSTRACT
The fast pace of economic growth in Kenya has created a large demand for meat products. This stands at an annual average of about 600,000 metric tonnes of red meat which is expected to continue rising according to global animal product consumption trends. Consequent challenges in management of increasing volumes of high strength wastewater have necessitated ardent research into sustainable technologies, for which vertical flow wetlands offer a promising solution. Three month experimentation conducted at Egerton University, explored the potential for use of vertical flow constructed wetlands in removing organic matter from slaughterhouse wastewater. The wastewater used was sourced from a mid-scale size slaughterhouse in Njoro Township. Experimental design consisted of three tanks of 2 mm sand, 8 mm quarry dust and 16 mm gravel at shallow 0.65 m and deeper 0.8 m depths, each with four replicates. Retention times of 1, 3 and 5 days were also investigated. The tanks were operated batch-wise and effluent water samples collected five times for each retention time studied. The water samples were analysed soon after using standard protocols for BOD5, COD, NH4-N and TSS. The untreated slaughter house wastewater characteristics ranged between 28,336-3,2502 mg/L for COD, 2,070-3,653 mg/L BOD5,1,371- 2,160 mg/L TSS and 52.98-52.42 g/L NH4-N. The results from the experimental mesocosm treatment set-up demonstrated that organic matter removal was highest at 5 day retention time, with removals of about 50%, 55% and 82% for BOD5, COD and TSS respectively. Deeper 0.8m mesocosms were noted to have significant differences in treatment for TSS and NH4-N compared to shallow 0.65 m mesocosms. Differences in substrate type were observed to have no significant effect on organic matter removal. In the case of ammonia, increase in substrate size was observed to decrease removal efficiency, although significant nitrification did not occur. NH4-N was observed to fluctuate with removal efficiency averaging at 26.5%. This study demonstrates that vertical flow wetlands operated at longer retention times and by tidal flow pattern facilitate removal of organic matter in slaughter house wastewater. However, a pre-treatment stage is necessary in order to reduce the organic matter load, and ensure lifecycle of the wetland is not threatened. Targeting ammonia reduction at the pre-treatment stage can highly increase the overall treatment efficiency.

CHAPTER ONE
INTRODUCTION
Background Information
In developing countries, it has been reported that release of untreated wastewater into rivers and streams poses a great risk to human and animal health in addition to degrading quality of surface and groundwater (Koech, Ogendi and Kipkemboi, 2012). High operational and maintenance costs associated with common chemically engineered treatment alternatives for wastewater are tremendous and more often than not, overwhelm the local authorities mandated to operate them. These challenges have necessitated a search for low cost yet efficient methods of waste water treatment for which Constructed Wetland (CW) technologies have shown great potential in east Africa (Oketch, A., 2002; Abira, A., 2008; Hunt, Riungu and Mathiu, 2011; Kimwaga, Mwegoha, Mhange, Nyomora and Ligali, 2013)

Verhoeven, Arheimer, Yin and Hefting, (2006) indicated that the use of constructed wetland technology can be of particular significance in the conservation of catchments, rivers and lakes especially because of their similarity in function to natural wetlands. As such, they have the added benefit of increasing natural habitats. Morel and Diener, (2006) also pointed out that CW technologies show great promise in inter-alia, reducing the agricultural use of much needed drinking water, reducing cost of water, increasing food security and improving public health.

Previous studies have established that constructed wetlands can be successfully used in the treatment of large scale industrial wastewater (Bojcevska, H., and Tonderski, K., 2007; Al Jawaheri, 2011; Lavrova and Koumanova, 2013; Chunkao et al., 2014) and domestic waste water (Vymazal, 2010; Gikas and Tsihrintzis, 2012; Lavrova and Koumanova, 2013). These evidences notwithstanding, little information exists on the treatment efficiency of CW systems in tropical regions. In addition, there are no documented CW systems treating slaughterhouse wastewater in Kenya. Noting further, very few studies exist regarding the application of vertical sub-surface flow constructed wetlands (VSSFCWs) to meat industry wastewater (Johns, 1995). This is despite the fact that vertical flow wetland technologies have been proven to efficiently remove high organic loads which are a major challenge for slaughterhouse wastewater (Stefanakis and Tsihrintzis, 2012; Lavrova and Koumanova, 2013, Chunkao and Dumpin, 2015). Considering that VSSFWs are also smaller than Horizontal Flow systems, they are a cost effective alternative. There is great value therefore, in conducting further studies on VSSFWs to fill existing gaps in their application on abattoir wastewater.

Statement of the problem
The fast pace of economic growth in developing nations like Kenya has created a large demand for meat products. A livestock revolution attributable to rising incomes and protein based diets has seen meat consumption triple in the global south (Delgado, 2003). The consequent intensification of meat production and animal agriculture to meet this demand is said to be putting significant pressure on freshwater ecosystems (Mekonnen and Hoekstra, 2012). Studies by the (World Bank Group, 2007) indicate that slaughterhouses typically consume between 2.5 m3 to 40 m3 of water per metric tonne of meat produced. Wastewater produced from slaughterhouse processes is usually a mixture of cleaning water of the facility and processing water from slaughtering and cleaning of guts. About 1200L are used for mid-sclae facility cleaning while 250 L of fresh water is used per carcass. A large volume of wastewater with high organic load is the result.

Predications by (Bouwman et al., 2013) indicate that this trend will continue to increase steadily until 2050. Slaughterhouses have therefore been presented with a unique challenge of managing increasing volumes of high strength wastewater. In most cases, raw or partially treated effluent is discharged directly into aquatic ecosystems. Occasionally, disposal mechanisms such as exhauster services are employed by some facilities. Poor management of slaughter house wastewater in general poses a very big threat to aquatic life due to the competition for dissolved oxygen created. Vertical flow wetlands present an efficient and cost effective solution to organic rich wastewater such as those generated from slaughterhouses, but knowledge gaps exist on their design and use in slaughterhouse wastewater management.

Objectives
General objective
To assess the potential use of vertical subsurface flow wetlands in treatment of slaughterhouse wastewater using mesocosm setup.

Specific objectives
1. To assess temporal variation in the physico-chemical characteristics of slaughterhouse wastewater over the study period.

2. To determine the effect of substrate type and depth on organic matter removal efficiency of slaughterhouse wastewater using a mesocosm experimental setup.

3. To assess the effect of different HRTs on removal efficiency of BOD5, COD, TSS and NH4-N.

Hypotheses
H0: There is no significant variation in physico-chemical characteristics of slaughterhouse wastewater over time.

H0: Differences in substrate type and depth have no significant effect on organic matter removal efficiency of slaughterhouse wastewater.

H0: Variation of HRTs does not have a significant influence on removal efficiency of BOD5, COD, TSS and NH4-N

Justification
Following incidences of poor surface water quality and foul odour in peri-urban areas of Dagoretti, Kenya as the results of untreated slaughterhouse wastewater, the National environmental Management Authority (NEMA) ordered closure of all slaughterhouses discharging raw effluent into aquatic receptacles (Kiplagat, 2008). Legal efforts by NEMA, (2006 a and b) compelling large water consuming enterprises to recycle their wastewater to set standards before release into the environment, have necessitated research into cost effective technologies involved in the pre- treatment of wastewater. Large scale operations without proper pre-treatment facilities for their wastewater were forced to shut down or invest in the same (Shiundu and Mwai, 2008).

Evidences strongly indicating that VFCWs have the ability to efficiently treat high loads of concentrated industrial pollutants such as slaughterhouse wastewater (WW) may provide a much needed solution. Conversely, their application in East Africa for treatment of slaughterhouse wastewater remains low. In the case of Kenya, it is perhaps because of the waste’s bio-chemical complexity combined with a scanty knowledge base on system design and operational mechanisms. The unpredictable treatment behaviour of CWs in general further points to existing knowledge gaps that hinder optimization of this technology. Also, existing literature elaborates extensively on the more popular conventional alternatives for slaughterhouse WW management. Not to mention that, the largest proportion of studies conducted on slaughterhouse WW is of temperate regions, hence cautioning on replicability of findings to temporal regions.

The small size requirements and characteristic design and operation aspects which enhance an aerobic environment make VFCWs a potentially sustainable technology for high organic matter breakdown. This in addition to the limitations mentioned above make it of great importance to advance existing studies on design and operational factors that optimize VFCWs’ ability to effectively reduce organic load, which happens to be a significant component of slaughterhouse WW.

Structure of thesis
Chapter one introduces the study, giving a general perspective of the problem in developing nations then narrowing down to specific cases in Kenya. It also highlights the scope of the problem and supports significance of the study. The section also highlights specific research inquiry and provides hypotheses aimed at answering these questions.

Chapter two details the general characteristics of slaughterhouse wastewater observed in different studies. It also looks at the conventional treatment options used for management of abattoir waste and finally narrows down to the specific use of vertical flow wetlands. It described various design and operation aspects that are important in achieving high treatment efficiency and also outlines removal processes and some of their affecting factors.

Chapter three describes the area of study and location of experiment site. The chapter further outlines the experimental setup design used, methods of sampling, water collection, laboratory analysis and finally the statistical analyses applied for output generation and presentation.

Chapter four details results obtained for the study, presented as tables and graphs according to the objectives under investigation.

Chapter five discusses the results and expounds on them in relation to past and present studies. It highlights similarities and differences of the findings with those of other researches.

Chapter six concludes on the findings of the study and provides recommendations for further action.

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Item Type: Kenyan Material  |  Attribute: 71 pages  |  Chapters: 1-5
Format: MS Word  |  Price: KSh900  |  Delivery: Within 30Mins.
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