Anaerobic treatment of slaughterhouse wastewater: a review

Effect of operational parameters on the performance of an anaerobic sequencing batch reactor (AnSBR) treating protein-rich wastewater

Treating protein-rich wastewater using cost-effective and simple-structured single-stage reactors presents several challenges. In this study, we applied an anaerobic sequencing batch reactor (AnSBR) to treat protein-rich wastewater from a slaughterhouse. We focused on identifying the key factors influencing the removal of chemical oxygen demand (COD) and the settling performance of the sludge. The AnSBR achieved a maximum total COD removal of 90%, a protein degradation efficiency exceeding 80%, and a COD to methane conversion efficiency of over 70% at organic loading rates of up to 6.2 g COD L-1 d-1. We found that the variations in both the organic loading rate within the reactor and the hydraulic retention time in the buffer tank had a significant effect on COD removal. The hydraulic retention time in the buffer tank and the reactor, which determined the ammonification efficiencies and the residual carbohydrate concentrations in the reactor liquid, affected the sludge settleability. Furthermore, the genus Clostridium sensu stricto 1, known as protein- and lipids-degraders, was predominant in the reactor. Statistical analysis showed a significant correlation between the core microbiome and ammonification efficiency, highlighting the importance of protein degradation as the governing process in the treatment. Our results will provide valuable insights to optimise the design and operation of AnSBR for efficient treatment of protein-rich wastewater.

Identification of some microbial flora contained in slaughterhouse effluent and likely to be effective in its treatment by biological process

The specific contributions of the different bacterial flora during the biological treatment of slaughterhouse effluents remain unclear. The objective of this study is to identify the different microbial flora which mainly contribute to the efficiency of the biodegradation of the organic, nitrogenous and phosphate loads contained in the slaughterhouse effluent during its biological treatment. To achieve this, the effluent to be treated was sampled from three slaughterhouses in the city of Ngaoundéré (Cameroon). The various effluents underwent a physicochemical and microbiological characterization. The effluent was subjected to biological treatment. The biodegradation process (biological treatment) took place in two reactors, each operating in batch. One of the two reactors was supplied with oxygen (aeration). The effluent being treated underwent a physicochemical and microbiological characterization for 30 days. The results obtained show organic matter and ammonium contents >1,000 mgO2/L in each of the three effluents. Bacillus cereus (69 × 108 CFU/mL), Pseudomonas aeruginosa (201 × 107 colony forming unit (CFU)/mL) and Yeasts (101 × 106 CFU/mL) globally constitute the majority of microbial groups among the seven microorganisms identified in the effluents of the three slaughterhouses. There is no real oxygenation effect of the medium on the growth of the three microbial flora during the treatment.

Effect of Hydraulic retention time on performance of anaerobic membrane bioreactor treating slaughterhouse wastewater

Slaughterhouse wastewater is a major environmental concern in many Vietnamese cities due to its high organic content and unpleasant odor. This study aimed to evaluate performance of a submerged flat sheet Anaerobic membrane bioreactor (AnMBR) system at different hydraulic retention time (HRT, 8-48 h) treating wastewater from a slaughterhouse in Hanoi City (Vietnam) at ambient temperature. The wastewater characteristics were as follows: chemical oxygen demand (COD) of 910 ± 171 mg/L; suspended solids (SS) of 273 ± 139 mg/L; and total nitrogen (T-N) of 115 ± 31 mg/L. The AnMBR system achieved high removal efficiencies for SS (99%) and COD (>90%) at an optimum HRT of 24 h. The biomethane yield reached 0.29 NL CH4/g CODinf. Importantly, the system maintained stable operation without flux decay and membrane fouling. HRT longer than 24 h could offer the better effluent quality without an increase in transmembrane pressure (TMP); however, it led to a lower methane production rate. Shorter HRT of 8-12 h caused a high TMP over -10 kPa, posing a risk for membrane fouling and biomass loss during cleaning, thus resulting in a low methane production. Our results suggest that AnMBR can be a reliable technology for wastewater treatment, reuse and energy recover from slaughterhouse wastewater in Vietnam and other similar climate countries.

Efficacious degradation of ethylene glycol by ultraviolet activated persulphate: reaction kinetics, transformation mechanisms, energy demand, and toxicity assessment

Ethylene glycol or 1,2-ethanediol (EG) is a persistent and toxic substance in the environment and extensively applied in petrochemical, surfactants, antifreeze, asphalt emulsion paints, cosmetics, plastics, and polyester fiber industries. Degradation of EG by using ultraviolet (UV) activated hydrogen peroxide (H2O2) and persulfate (PS) or persulfate anion (S2O82-) based advanced oxidation processes (AOPs) were explored. The result obtained demonstrate that UV/PS (85.7 ± 2.5%) has exhibited improved degradation efficiency of EG as compared to UV/H2O2 (40.4 ± 3.2%) at optimal operating conditions of 24 mM of EG concentration, 5 mM of H2O2, 5 mM of PS, 1.02 mW cm-2 of UV fluence, and pH of 7.0. Impacts of operating factors, including initial EG concentration, oxidant dosage, reaction duration, and the impact of different water quality parameters, were also explored in this present investigation. The degradation of EG in Milli-Q® water followed pseudo - first order reaction kinetics in both methods having a rate constant of about 0.070 min-1 and 0.243 min-1 for UV/H2O2 and UV/PS, respectively, at optimum operating conditions. Additionally, an economic assessment was also conducted under optimal experimental conditions, and the electrical energy per order and total operational cost for treating per m3 of EG-laden wastewater was observed to be about 0.042 kWh m-3 order-1 and 0.221 $ m-3 order-1, respectively, for UV/PS, which was slightly lower than UV/H2O2 (0.146 kWh m-3 order-1; 0.233 $ m-3 order-1). The potential degradation mechanisms were proposed based on intermediate by-products detected by Fourier transform infrared (FTIR) spectroscopy and gas chromatography-mass spectroscopy (GC-MS). Moreover, real petrochemical effluent containing EG was also treated by UV/PS, demonstrating 74.7 ± 3.8% of EG and 40.7 ± 2.6% of total organic carbon removal at 5 mM of PS and 1.02 mW cm-2 of UV fluence. A toxicity tests on Escherichia coli (E. coli) and Vigna radiata (green gram) confirmed non-toxic nature of UV/PS treated water.

Performance evaluation and kinetics modeling of a hybrid UASB reactor treating bovine slaughterhouse wastewater

This work aimed to analyze the performance of a hybrid upflow anaerobic sludge blanket (HUASB) reactor packed with natural zeolite for slaughterhouse wastewater treatment through kinetics modeling. Wastewater samples from a municipal bovine slaughterhouse were sieved through a 1-mm mesh screen and thermally pretreated in an autoclave. Then, biological treatment was carried out in a HUASB reactor packed with a zeolite filter at the top. Slaughterhouse wastewater was diluted with municipal wastewater during the start-up period to achieve a low organic loading rate (OLR) (3.4 kg chemical oxygen demand (COD)/m3/day); afterward, it gradually increased until dilution was eliminated, reaching 14.4 kg COD/m3/day. At this OLR, the maximum percentage removals of total COD, soluble COD, total solid, and volatile solid (67.7%, 68.3%, 55.2%, and 72.1%, respectively) were found. Moreover, the zeolite filter enabled NH4+-N and PO43--P removal, with the highest values (32.8% and 35%, respectively) at 9.8 kg COD/m3/day. Thus, the natural zeolite filter improved the reactor's performance. Among all equations analyzed, the modified Stover-Kincannon equation correctly fitted the results and provided the best prediction of the HUASB reactor's performance.

Screening plant growth effects of sheep slaughterhouse waste-derived soil amendments in greenhouse trials

Ameliorative effects of sheep slaughterhouse waste-derived soil amendments (struvite, blood meal, bone meal) were explored and quantified by a series of comparative greenhouse trials. A scoring matrix system was developed for 25 different test plants using 300 agricultural measurements obtained for three basic growth parameters (fresh-dry plant weights and plant heights) and four different fertilizer sources including solid vermicompost. More than 70% of NH₄⁺-N recovery from sheep slaughterhouse wastewater was achieved using a chemical combination of MgCl₂.6H₂O + NaH₂PO₄.2H₂O, a molar ratio of Mg²⁺:NH₄⁺-N:PO₄^3-P = 1.2:1:1, a reaction pH of 9.0, an initial NH₄⁺-N concentration of 240 mg/L, and a reaction time of 15 min. According to SEM micrographs, surface morphology of struvite exhibited a highly porous structure composed of irregularly shaped crystals of various sizes (11.34-79.38 μm). FTIR spectroscopy verified the active functional groups on the proximity of all fertilizer sources within the spectral range of 500-3900 cm^-1. TGA-DTG-DSC thermograms of struvite revealed that the mass loss occurred in two temperature regions and reached a maximum mass loss rate of 1.63%/min at 317 °C. The average percentages of increase (57.55-100.62%) and performance points (69-79) corroborated that the fertility value of struvite ranked first on average in cultivation of the analyzed plant species. Findings of this agro-valorization study confirmed that sheep slaughterhouse waste-derived fertilizers could be a beneficial way to promote bio-waste management and environmentally friendly agriculture.

Enhanced treatment of organic matter in slaughter wastewater through live Bacillus velezensis strain using nano zinc oxide microsphere

Slaughter wastewater is an important and wide range of environmental issues, and even threaten human health through meat production. A high efficiency and stability microsphere-immobilized Bacillus velezensis strain was designed to remove organic matter and inhibit the growth of harmful bacteria in process of slaughter wastewater. Bacillus velezensis was immobilized on the surface of sodium alginate (SA)/Polyvinyl alcohol (PVA)/Nano Zinc Oxide (Nano-ZnO) microsphere with the adhesion to bio-carrier through direct physical adsorption. Results indicated that SA/PVA/ZnO and SA/ZnO microspheres could inhibit E.coli growth with adding 0.15 g/L nano-ZnO and not affect Bacillus velezensis strain, and the removal the chemical oxygen demand (COD) rates of SA/PVA/ZnO microsphere immobilized cells are 16.99%, followed by SA/ZnO (13.69%) and free bacteria (7.61%) from 50% concentration slaughter wastewater within 24 h at 37 °C, pH 7.0, and 120 rpm, a significant difference was found between the microsphere and control group. Moreover, when the processing time reaches 36 h, COD degradation of SA/PVA/ZnO microsphere is obviously higher than other groups (SA/PVA/ZnO:SA/ZnO:control vs 18.535 : 15.446: 10.812). Similar results were obtained from 30% concentration slaughter wastewater. Moreover, protein degradation assay was detected, and there are no significant difference (SA/PVA/ZnO:SA/ZnO:control vs 35.4 : 34.4: 36.0). The design of this strategy could greatly enhance the degradation efficiency, inhibit the growth of other bacteria and no effect on the activity of protease in slaughter wastewater. These findings suggested that the nano-ZnO hydrogel immobilization Bacillus velezensis system wastewater treatment is a valuable alternative method for the remediation of pollutants from slaughter wastewater with a novel and eco-friendly with low-cost investment as an advantage.

Effects of Seasonal Temperature Variation on Slurry Temperature and Biogas Composition of a Commercial Fixed-Dome Anaerobic Digester Used in Bangladesh

Biogas is produced in Bangladesh mostly through fixed-dome anaerobic digesters, which usually operate without any temperature controller. An experiment was conducted to monitor the seasonal temperature variation inside a fixed-dome type digester and its effect on biogas composition. A commercial-scale digester with a working volume of 350 m3 was used for this study. Three k-type thermocouple sensors were used to monitor the ambient, biogas, and slurry temperatures in real-time. The results showed that the average ambient temperature in the autumn, late autumn, and winter was 29.05, 22.90, and 17.64 °C, respectively. The average slurry temperature in the autumn (30.38 °C) was higher than in the late autumn (29.36 °C) and in the winter (25.76 °C). The highest and lowest slurry temperatures were found to be 31.11 and 24.47 °C, respectively, which indicated that the digester worked within a wide temperature range, establishing both psychrophilic and mesophilic operational conditions. Higher methane concentrations were observed in the autumn than in the late autumn and winter. The CO2 and H2S concentrations were higher in the winter than those of in the autumn and late autumn. The electricity generation in the winter was 47.85% and 45.15% lower than in the autumn and late autumn, respectively.