###### Abstract  
Poultry slaughterhouse wastewater contains high concentrations of chemical oxygen demand (COD), total suspended solids (TSSs), fats, oil and grease (FOG), proteins and carbohydrates. It is important that the wastewater is treated to acceptable environmental discharge standards. In this study, the poultry slaughterhouse wastewater (PSW) was treated using two-stage processes consisting of a biological pre-treatment using a biodegradation agent (Eco-flushTM) coupled with a down-flow expanded granular bed reactor (DEGBR). The results showed that the biological pre-treatment was observed to be highly effective for removal of FOG, COD and TSS with a removal efficiency of \(80\pm 6.3\%\), \(88\pm 8.4\%\) and \(56\pm 7.2\%\), respectively. The DEGBR showed a stable performance in terms FOG, COD and, TSS removal, with average removal efficiencies of \(89\pm 2.8\%\), \(87\pm 9.5\%\), and \(94\pm 3.7\%\), respectively. The overall removal rate performance of the integrated system of pre-treatment and DEGBR in terms FOG, COD and TSS, was \(97\pm 0.8\%\), \(92\pm 6.3\%\) and \(97\pm 1.2\%\). Furthermore, the average volatile fatty acid/alkalinity (VFA/Alkalinity) ratio of 0.2 was reported, which indicated that the DEGBR was stable throughout the operation. chemical oxygen demand (COD); fats oil and grease (FOG); total suspended solids (TSSs); poultry slaughterhouse wastewater (PSW); down-flow expanded granular bed reactor (DEGBR) +
Footnote †: journal: Applied Sciences
South Africa (SA) in the past decade. The nature of the activities associated with clean water usage during washing and poultry product processing culminates in the release of a tremendous volume of wastewater [6]. The vast generation of PSW also presents itself as a potential threat to the ecosystem, as well as human health. Therefore, the implication of untreated organic substances, such as blood and feathers, would result in the eutrophication of receiving surface water, thereby causing environmental pollution and a health hazard on people exposed to it [7]. Ordinarily, poultry slaughterhouse processes involve a series of processing steps ranging from the slaughtering of live birds to the conversion of the live birds to edible meat fit for human consumption [1]. The latter processing steps require large volumes of freshwater, and this contributes to the pollution of the freshwater sources if the PSW is released untreated. The high volume of water utilized in such facilities stems from various processing steps requiring potable water because of the need to provide safe products [8]. To treat the PSW, suitable bioreactors are needed. Most reactors have operational challenges which range from clogging, longer processing time and lower efficiencies [9]. However, one of the most successful and effective process equipment used in the treatment of wastewater is the static granular bed reactor (SGBR) [10]. In the SGBR, PSW is fed at the top of the reactor where it flows downward via a bed of anaerobic granules. However, some problems may be encountered during the operation of the SGBR, including clogging and sludge wash-out, which are caused by high and excessive concentrations of biomass growth [7]. The excessive concentration of biomass growth generally leads to lower COD removal efficiencies. An important aspect that can assist in the treatment of PSW is the use of a novel bioremediation agent called Eco-flushTM in the pre-treatment step, which is followed by the down-flow expanded granular bed reactor (DEGBR). The DEGBR was designed to mitigate the challenges experienced by the SGBR [11]. The DEGBR is a modified adaptation of the SGBR that is fitted with a recycle stream on the side of the reactor, which is used for recycling effluent from the bottom of the reactor to the top [11]. This is meant to prevent issues such as flow channeling, to improve the distribution of the feed to the biomass, and to implement intermittent fluidization whenever it is required using a top-down recycling strategy.