In this study, the treatment of poultry slaughterhouse wastewater (PSW) was evaluated using two new down-flow high-rate anaerobic bioreactor systems (HRABS), including the down-flow expanded granular bed reactor (DEGBR) and the static granular bed reactor (SGBR). These two bioreactors have demonstrated a good performance for the treatment of PSW with removal percentages of the biochemical oxygen demand (BOD5), the chemical oxygen demand (COD), and fats, oil, and grease (FOG) exceeding 95% during peak performance days. This performance of down-flow HRABS appears as a breakthrough in the field of anaerobic treatment of medium to high-strength wastewater because down-flow anaerobic bioreactors have been neglected for the high-rate anaerobic treatment of such wastewater due to the success of up-flow anaerobic reactors such as the UASB and the EGSB as a result of the granulation of a consortium of anaerobic bacteria required for efficient anaerobic digestion and biogas production. Hence, to promote the recourse to such technologies and provide further explanation to their performance, this study approached the kinetic analysis of these two down-flow HRABS using the modified Stover-Kincannon and the Grau second-order multi-component substrate models. From a comparison between the two models investigated, the modified Stover-Kincannon model provided the best prediction for the concentration of the substrate in the effluent from the two HRABS. This analysis led to the determination of the kinetic parameters of the two models that can be used for the design of the two HRABS and the prediction of the performance of the SGBR and DEGBR. The kinetic parameters determined using the Modified Stover-Kincannon were Umax = 40.5 gCOD/L.day and KB = 47.3 gCOD/L.day for the DEGBR and Umax = 33.6 gCOD/L.day and KB = 44.9 gCOD/L.day for the SGBR; while, using the Grau second-order model, the kinetic models determined were a = 0.058 and b = 1.112 for the DEGBR and a = 0.135 and b = 1.33 for the SGBR.
The anaerobic decomposition of coconut endosperm waste (CEW), residue derived from cooking, has been insidiously spewing greenhouse gasses. Thus, the bioconversion of CEW via in situ fermentation by exo-microbes from commercial Rid-X and subsequent valorization by black soldier fly larvae (BSFL) was the primary objective of the current study to gain sustainable larval lipid and protein. Accordingly, various concentrations of exo-microbes were separately homogenized with CEW to perform fermentation amidst feeding to BSFL. It was found that 2.50% of exo-microbes was the threshold amount entailed to assuage competition between exo-microbes and BSFL for common nutrients. The presence of remnant nutrients exuded from the fermentation using 2.50% of exo-microbes was confirmed to promote BSFL growth measured as maximum larval weight gained and growth rate. Although the BSFL could accumulate the highest protein (16 mg/larva) upon feeding with CEW containing 2.50% of exo-microbes, more lipid (13 mg/larva) was stored in employing 0.10% of exo-microbes because of minimum loss to metabolic processes while prolonging the BSFL in its 5th instar stage.
Sewage sludge has long been regarded as a hazardous waste by virtue of the loaded heavy metals and pathogens. Recently, more advanced technologies are introduced to make use of the nutrients from this hazardous sludge. Successful recovery of sludge's carbon content could significantly convert waste to energy and promote energy sustainability. Meanwhile, the recovery of nitrogen and trace minerals allows the production of fertilizers. This review is elucidating the performances of modern thermal treatment technologies in recovering resources from sewage sludge while reducing its environmental impacts. Exhaustive investigations show that most modern technologies are capable of recovering sludge's carbon content for energy generation. Concurrently, the technologies could as well stabilize heavy metals, destroy harmful pathogens, and reduce the volume of sludge to minimize the environmental impacts. Nevertheless, the high initial investment cost still poses a huge hurdle for many developing countries. Since the initial investment cost is inevitable, the future works should focus on improving the profit margin of thermal technologies; so that it would be more financially attractive. This can be done through process optimization, improved process design as well as the use of suitable co-substrates, additives, and catalyst as propounded in the review.