Poultry slaughterhouse wastewater treatment using bio-physico-pretreatment systems coupled with an expanded granular bed reactor

Abstract

Poultry slaughterhouse wastewater (PSW) is having a high organic matter content which contains constituents such as blood, undigested food, meat debri and feathers, colloidal particles as well as soluble proteins. This type of wastewater in turn is high in fats, oils and grease (FOG), chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solids (TSS) and volatile fatty acids (VFA) from slaughtering and facility cleaning activities which when released untreated end-up in drinking water sources. The poultry industry is therefore mandated through stringent environmental rules to treat the wastewater to acceptable contaminant levels and to reduce the amount of wastewater that is released into natural water sources. As such, a variety of treatment processes are used by the poultry industry to reduce the discharge of untreated wastewater into the environment. These processes include physical, chemical and biological treatment processes. Biological treatment processes are nontoxic, and produce extracellular, biopolymeric substances secreted by algae, yeast, and bacteria in the processes for numerous purposes. Due to these properties and the lack of secondary pollution, biological remediation has been identified as an alternative to chemical and physical treatment options. This research was aimed to determine whether pretreating the PSW with a commercially produced product, i.e., Eco-FlushTM which is a biodelipidation agent, would result in the reduction of COD, FOG and TSS and therefore allow optimal treatment of the PSW using an Expanded Granular Sludge Bed (EGSB) reactor, an anaerobic bioreactor selected for this study. A volume (250 L) of the PSW was collected from a poultry slaughterhouse using sterile 25L polypropylene bottles and stored at 4˚C. The raw PSW was analyzed for FOG, COD, and TSS prior to the addition of the PSW to the pretreatment tank. The PSW was pretreated by mixing 20 mL Eco-FlushTM mixed into 20L of raw PSW. The mixture was aerated for 24 h then allowed to settle for a further 24 h to allow the Eco-FlushTM time to properly hydrolyze FOG and flocculate-coagulate proteins including TSS within the PSW and reduce the level of dissolved oxygen (DO) in the PSW prior to it being supplied to the EGSB reactor operated at 37 ˚C. The pretreated PSW was then filtered to remove feathers, pieces of meat and the flocculated organic matter was skimmed off such that clogging will be minimized in the EGSB bioreactor. The EGSB reactor containing a slurry of activated sludge, milk as a substrate and PSW was also allowed to acclimatize for 3 days, for bacterial growth to be at an exponential phase, prior to feeding the EGSB reactor with pretreated PSW from the pretreatment tank. The EGSB reactor was initially fed PSW for 16 h a day for one month to allow the activated sludge to adapt to the new feed and for proper optimization of the plant’s operational parameters. The system was then run continuously, for 7 days a week, over a period of four months, with 2L samples being collected three times a week namely Monday, Wednesday and Friday from the pretreated PSW and the effluent from the EGSB bioreactor. The PSW’s FOG, COD and TSS content was determined to assess the effectiveness of the pre-treatment process, EGSB bioreactor anaerobic treatment to observe the remedial action of the combined pre-treatment-EGSB system. The average removal in the pretreatment tank for COD, FOG and TSS was 43%, 66% and 59%, respectively. The EGSB recorded upper limits of 76% COD removal, upper limits of 96% were recorded for TSS and FOG removal peaked at 97% with an average of 66%. An increased treatment efficacy was noted for the combined PSW treatment system, whereby the COD, FOG and TSS removal averaged 76%, 88% and 87%, respectively. The process developed is intended for micro, small and medium poultry slaughterhouses.