Anaerobic digestion of high strength wastewater in high rate anaerobic bioreactor systems: case of Poultry Slaughterhouse Wastewater (PSW)

Abstract

Considering global and local challenges such as water scarcity, the pollution of surface water, the proliferation of water-borne diseases, and levies imposed by municipal Councils to industries for the discharge of untreated wastewater, it becomes essential for industries to select and implement enhanced wastewater treatment strategies geared towards reducing the concentration of contaminants and benefiting from the organic content of their effluent, if applicable and depending on the selected treatment process. An interesting option for the treatment of organic-laden wastewater, such as poultry slaughterhouse wastewater (PSW), is high rate anaerobic digestion. The latter has become popular since the development of configurations aimed at promoting a long solid retention time (SRT) for short hydraulic retention times. This thesis elaborates on the treatment of poultry slaughterhouses effluent with three high rate anaerobic bioreactors systems (HRABS), including the Down-flow Expanded Granular Bed Reactor (DEGBR), the Expanded Granular Sludge Bed (EGSB) reactor, and the Static Granular Bed Reactor (SGBR). Moreover, it motivates the selection of HRABS for the treatment of PSW, after discussing different processing options for the conversion of different poultry slaughterhouses solid wastes into marketable by-products. Before selecting these HRABS, the PSW was analyzed, characterized and specific key water quality assessment parameters (tCOD, BOD5, and FOG) were correlated towards the reduction of cost, time, and chemical waste generated from these analyses. Subsequently, to ensure conducive operation in down-flow HRABS (DEGBR and SGBR) relying on the support of an underdrain system to enable the retention of the required anaerobic biomass and the steady circulation of the HRABS’ effluent, some packing materials (white pebbles, pea gravel, small-sized pumice stones, Ceramic marbles, and medium-sized pumice stones) were selected and evaluated. These were initially selected based on their inertness, affordability, and availability. Additionally, further suitability assessment parameters were defined and used for the selection of the most suitable packing material for the underdrain system. These parameters included their porosity, their permeability, their anaerobic sludge retention capacity, and their induced pressure loss. The medium-sized pumice stones showed the best suitability for the underdrain system with the lowest induced pressure loss, and the highest permeability, porosity and anaerobic sludge retention capacity. The selection of the most suitable packing material led to the operation and the assessment of the DEGBR, which showed a good performance for the treatment of PSW, with tCOD, BOD5, and TSS average removal percentages >95%, and a FOG average removal percentage of 93.67 ± 4.51%, for an organic loading rate varying between 1.1 to 38.9 gCOD/L.day. Subsequently, the performance of the SGBR and EGSB was also investigated for the treatment of PSW. The EGSB also provided good results with 99.1%, 99.5%, and 97%, for the removal of tCOD, BOD5 and FOG, respectively. At last, the SGBR achieved tCOD, BOD5 and FOG percentage removal of 97.6%, 99.2%, and 97.7%, respectively. This good performance of down-flow HRABS led to recourse to the modified Stover-Kincannon and the Grau Second-order kinetic models for the prediction of the DEGBR and the SGBR, as well as their plant footprint. This study provided the best prediction of the performance of the down-flow HRABS with the modified Stover-Kincannon model.