TREATMENT STRATEGY OF SLAUGHTERHOUSE WASTEWATER

Abstract

Meat processing is an important food processing industry catering to 60% of world's population. This industry is comprised of the slaughtering and processing of cattle, sheeps, goats, buffaloes, pigs etc. Wastewater from slaughterhouses varies widely in composition, strength and flow. Often, the pollution load from two similar abattoir units is different primarily due to the differences in processing activities, animal species and wastewater management. Slaughterhouse wastewater (SI IWW) is a moderate to low strength complex wastewater. The wastes arc organic, biologically dcgradable with relatively high concentrations of solids and fat. Most of the organic strength in the effluent comprised of the blood fraction of the generated waste. Of the pollutants, 40-50% are insoluble, slowly biodegradable suspended solids. India has the largest animal population in the world with 430 million, but it is one of the most unproductive in the world, according to world bank estimates. In India, meat production has not yet reached the status of an industry. Experts point out that animal husbandry has been a neglected area. Animals are slaughtered in small slaughterhouses or abattoirs. Most of them are built in the early years of this century and are in a dilapidated condition, without basic facilities. Meat is produced in the most unhygienic condition. The problem of disposal of waste from these slaughterhouses is a vexing issue, as the waste is being disposed off in a primitive fashion causing insanitary conditions. In butchery's located at Delhi, Calcutta, Madras and Bombay on an average of 8-12 thousand animals are killed per day. The wastewater generally is discharged directly into municipal sewers. Foul stench pervades areas around the abattoir. It is a health hazard to those working and residing nearby. Recently the environmental/social organisations protested against the insanitary conditions prevailing at Delhi, Bangalore and Hyderabad. These organisations demanded for relocation of abattoirs away from the city centres. Karnataka government recently announced plans for modernising the abattoirs in the state. In the proposed scheme, animals would be slaughtered in rural-based abattoirs, and only carcasses would be brought to consuming points in towns in air cooled or refrigerated vans. The space vacated by existing abattoirs can be utilised for dressing and distribution of meat to butchers. Treatment of the SHWW to bring down the pollutants to a level so that the waste can bedisposed offsafely without affecting the recieving body should also bethe integral part of the modernisation of abattoirs programme. The primary treatment by physical and/or chemical methods and biological methods are employed for the treatment of SHWW. Though the anaerobic systems provide a complete treatment, the anaerobic methods are popularly used because of the advantage of resource recovery. Moreover, aerobic systems require the use of pure oxygen, which not only adds to the treatment costs but places a heavy reliance on an external source of supply for a key element of the process. Conventional anaerobic treatment methods are not considered favourable for treatment of industrial effluents as they require long detention periods necessitating larger reactor volumes. These draw-backs led to the development of high rate anaerobic methods and better reactor configurations which work at very low hydraulic retention time (HRT) in comparison to solids retention time (SRT). Pilot and bench scale studies have been carried out to treat SHWW using non-conventional biological systems such as rotating biological contactor, anaerobic filter, fixed bed reactor, fluidized bed biofilm reactor, continuous stirred tank reactor, anaerobic fluidized bed reactor and upflow anaerobic sludge blanket reactor. These methods, however, are still in investigative stage and have not been used as full scale plants for treating SHWW. Amongst the several non-conventional biological methods, the upflow anaerobic sludge blanket (UASB) process appears to be an attractive system for the treatment of SHWW owing to the fact that the process is able to maintain a sufficient amount of viable sludge, thereby providing efficient and stable treatment. It also offers the advantage of requiring no support material and energy recovery. However, fat concentration (125-675 mg l"1) in the SHWW is likely to hinder the anaerobic digestion process. Therefore, the installation of a good fat separator prior to a UASB reactor is necessary. In the case of meat wastes dissolved air flotation (DAF) process is quite efficient because of high effluent quality and minimised odour nuisance. Compounding these factors into consideration, (iii) investigations have been carried out : (i) to explore a combination of DAF-UASB unit for the treatment of SHWW. (ii) to systematically evaluate Biochemical methane potential (BMP) ofraw, fat and soluble organic fractions of wastewater. (iii) to check the feasibility of treating SHWW mixed with sewage. • For convenience and clarity of presentation the subject matter of the thesis has been divided into following chapters. 1. INTRODUCTION 2. SLAUGHTERHOUSE WASTEWATER TREATMENT : STATE OF ART 3. DAF, ANAEROBIC TREATABILITY AND UASB : A REVIEW 4. MATERIALS AND METHODOLOGY 5. RESULTS AND DISCUSSIONS 6. DESIGN OF TREATMENT UNIT 7. CONCLUSIONS AND RECOMMENDATIONS In Chapter-I, the objectives of the work embodied in the thesis have been defined. It presents a brief background information on characteristics of SHWW, treatment methods in practice and the status of slaughterhouses in India. Meat processing operations, waste generation and characteristics ofSHWW and various physico-chemical and biological processes employed for treating SHWW in western countries and in India are widely discussed in Chapter-II. Chapter-Ill gives the detailed literature review on DAF process, serum bottle technique for BMP evaluation and UASB process. Literature reviewed covers the characteristic features, design parameters and applications of units/technique for the treatment of industrial effluents. Chapter-IV describes the materials and methods employed in the investigations. All the experiments were carried out on the wastewater collected from anearby butchery. DAF unit consisting of a saturator and a flotation chamber was fabricated. The performance was evaluated at (iv) different gauge pressure (Gp), air to solids ratio (A/S) and influent SS concentration. The same unit was later modified to countercurrent dissolved air flotation unit (CCDAF) for further explorations. BMP batch assay tests on various fractions of SHWW and SHWW in conjunction with a synthetic wastewater prepared from molasses (equivalent to sewage) carried out by using serum bottle technique of Owen, et al. (1979) are also presented along with continuous flow experiments carried out at a liquid temperature of 30 ± 1°C in two identical reactors of 11.4 1 capacity (R( and R^). The reactors were fed continuously with raw SHWW and subnatant from DAF unit. All analyses were done according to standard methods (APHA, 1991). The data obtained from the studies have been presented in Chapter-V. Discussions of the results are incorporated in the same chapter. The analysis of results has been performed to give information about potential and performance ofUASB and DAF-UASB systems, in treating SHWW. The performance evaluation and cost economic analysis of conventional DAF and countercurrent DAF process suggested the suitability of conventional DAF process with working gauge pressure of 7 kg cm2. An empirical non-dimensional 'Dilution Parameter' (DP) has also been devised. Using DP, the amount of saturator feed to be added to achieve the removal offat to an extent that it leaves the subnatant amenable for treatment by UASB can be calculated. The results of BMP test demonstrated the better degradability of subnatant than raw SHWW and float, and hence suggested the necessity of pre-treatment in conjunction with sewage. The better performance of UASB reactor in terms of COD removal and gas production with pre-treated waste compared to raw SHWW recommended the DAF-UASB system for the treatment of SHWW. Based on the findings given in Chapter-V, design of the proposed DAF-UASB system has been incorporated in Chapter-VI. The conclusions and limitations derived from the present study and scope for future investigations form the subject matter of Chapter-VII. (