Treatment of poultry slaughterhouse wastewaters by electrocoagulation

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Abstract

Treatment of poultry slaughterhouse wastewater (PSW) by electrocoagulation (EC) has been investigated batchwise in this paper. Effects of the process variables such as medium pH, electrode material, current density, and operating time are investigated on chemical oxygen demand (COD) and oil–grease removal efficiencies, electrical energy consumption, and sacrificial electrode consumption. The highest COD removal efficiency is reached with aluminum as 93%, and maximum oil–grease removal is obtained with iron electrodes as 98%. Combined use of both electrode materials in the EC unit may yield high process performances with respect to both COD and oil–grease removals. Further work needs to be carried out at pilot scale to assess the technical end economic feasibility of the process.

Introduction

The consumption of poultry products in Turkey, which constitute a significant part of all meat consumption, has steadily been increased in, reaching about 10 kg per capita in 2003. Poultry slaughterhouses produce large amounts of wastewater containing high amounts of biodegradable organic matter, suspended and colloidal matter such as fats, proteins and cellulose [1], [2], [3]. Because of legal restrictions, rising treatment costs, and environmentally conscious consumers, the treatment of wastewaters has emerged as a major concern not only in poultry processing but also in the meat industry in general.

Aerobic and anaerobic methods have been traditionally used for the treatment of PSW. Aerobic treatment processes are limited by their high energy consumption needed for aeration and high sludge production. The anaerobic treatment of PSW is often slowed or impaired due to the accumulation of suspended solids and floating fats in the reactor, which lead to a reduction in the methanogenic activity and biomass wash-out [2]. Furthermore, it is also reported that anaerobic treatment is sensitive to high organic loading rates, as a serious disadvantage [3], [4], [5]. Both biological processes require long hydraulic retention time and large reactor volumes, high biomass concentration and controlling of sludge loss, to avoid the wash-out of the sludge.

In recent years, new processes for efficient and adequate treatment of various industrial wastewaters with relatively low operating costs have been needed due to strict environmental regulations. At this point, the EC process has attracted a great deal of attention in treating industrial wastewaters because of its versatility and environmental compatibility. This method is characterized by simple equipment, easy operation, a shortened reactive retention period, a reduction or absence of equipment for adding chemicals, and decreased amount of precipitate or sludge which sediments rapidly. The process has been shown to be an effective and reliable technology that provides an environmentally compatible method for reducing a large variety of pollutants [6], [7], [8]. Moreover, during EC, the salt content of the liquid salt content does not increase appreciably, as in the case of chemical treatment [7].

EC has been proved to be an efficient method for the treatment of water and wastewater. It was tested successfully to treat textile wastewater [9], [10], [11], [12], [13], urban wastewater [14], landfill leachate [15], tar sand and oil shale wastewater [16], and chemical fiber plant wastewater [17]. EC has also been proposed to treat various food industry wastewaters such as, yeast wastewater [18], olive oil wastewater [19], [20], restaurant wastewater [21], [22], egg process wastewater [23], and oily wastewater [24], [25], [26].

Despite to the impressive amount of scientific research on the treatment of industrial wastewaters by EC, little research has been done on the treatment of PSW by means of EC [27], [28]. Thus, the purpose of the present study is to assess the performance of EC on the treatment of PSW, by exploring the effects of various process parameters such as sacrificial anode material, wastewater pH, current density, and treatment time, on the COD and oil–grease removal rates.

Section snippets

Wastewater source and characteristics

The wastewater used in this work was taken from a local poultry slaughterhouse plant with 45,000 chickens per day capacity, located in the city of Gebze (Turkey), producing approximately 450 tonnes of wastewater daily. The wastewaters emerging from various operations such as chicken cutting, scalding, defeathering, eviscerating, chilling, packing, and plant cleanup are collected in an equalization tank, after being filtered using a screen filter to remove hair and solids. The raw PSW mainly

Results and discussion

The efficiency of pollutant removal from wastewaters by EC process depends on several operating parameters: the type of electrode material, initial pH, current density or cell voltage, and processing time. In this study, in addition to COD removal percent, which is the primary criterium to assess the process performance, oil–grease removal percent, electrical energy and anode consumptions per cubic meter of wastewater also have been taken into consideration. The same runs are conducted with

Conclusions

EC is found to be an effective method for the treatment of PSW. As electrode material, aluminum electrode performs better in reducing the COD; low initial pH, such as 2–3, and current density of 150 A/m2 are preferable for having a high COD removal efficiency (93%) in 25 min. Low initial pH is not very crucial due to the fact that the final pH approaches near 5–6 as a result of the buffering capacity of the various process occuring in the unit. On the other hand, iron removes oil–grease with 98%

Acknowledgment

This study was supported by the Gebze Institute of Technology Research Fund (Grant No. 02B-03-03-03).

References (32)

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