Combinative treatment of phenol-rich retting-pond wastewater by a hybrid upflow anaerobic sludge blanket reactor and solar photofenton process

Resolution of conflict of reduced sludge production with EBPR by coupling OSA to A2/O process in a pilot scale SBR

The pinnacle of all the efforts of nutrient removal is practically put-down the moment biological cells are lysed, hydrolyzed or digested causing subsequent reappearance of assimilated nitrogen and phosphorus in any biological process. While sludge reduction requires high SRT, the enhanced phosphorus assimilative uptake demands low SRT. A novel reactor configuration for enhanced sludge and phosphorus removal was put to test by incorporating a side stream anaerobic reactor to an Anaerobic-Anoxic-Aerobic (A²O) SBR with a pre-anoxic chamber and an influent receiving inlet anaerobic reactor. The reactor was operated at the average and lowest range of prevailing carbon/phosphorus (C/P) ratio of 50 and 15 in the sewage. The phosphorus enrichment was 0.0469-0.135 mgTP/mgVSS resulting in 1.76-5.05-fold increase from cellular content by virtue of maintaining sludge recycle from SBR aeration tank to side stream anaerobic reactor from 3.78 to 9.78 (average 4.4-8.2) gVSS/gVSS present in the reactor. However, the sludge was also reduced from 3% to 51% on an average basis during the same recirculation regime. This novel configuration consists of an inlet anaerobic reactor, one pre-anoxic chamber and one intermittent oxic anoxic reaction SBR and a side stream anaerobic reactor. The first anaerobic reactor at inlet followed by pre-anoxic chamber was provided for increased ortho-p released and nitrification respectively and a side stream anaerobic reactor for sludge reduction through sludge fasting mechanism. The EBPR and lesser sludge growth were two conflicting parameters reconciled to the extent that if sludge recycled up to 6.41 gVSS/gVSS the sludge growth would be reduced by 25% and phosphorus enrichment could be attained up to 3.46 times the stoichiometric value. Any further recirculation would reduce the sludge further but at the expense of enhanced phosphorus uptake as released phosphorus from side stream anaerobic reactor also recycled back to main SBR causing looping and at more than 6.41gVSSrecycled/gVSS it nullified the enhanced effect.

Anaerobic recalcitrance in wastewater treatment: A review

Anaerobic treatment is applied as an alternative to traditional aerobic treatment for recalcitrant compound degradation. This review highlighted the recalcitrant compounds in wastewaters and their pathways under aerobic and anaerobic conditions. Forty-one recalcitrant compounds commonly found in wastewater along with associated anaerobic removal performance were summarized from current research. Anaerobic degradability of wastewater could not be appropriately evaluated by BOD/COD ratio, which should only be suitable for determining aerobic degradability. Recalcitrant wastewaters with a low BOD/COD ratio may be handled by anaerobic treatments after the adaption and provision of sufficient electron donors. Novel indicator characterizing the anaerobic recalcitrance of wastewater is called for, essential for emergent needs to resource recovery from high-strength recalcitrant wastewater for fulfilling appeals of circular bioeconomy of modern societies.

Phase separated pretreatment strategies for enhanced waste activated sludge disintegration in anaerobic digestion: An outlook and recent trends

A significant ecological problem was developed on disposing the enormous amounts of waste activated sludge (WAS) produced by traditional wastewater treatment. There have been various attempts recently originated to develop innovative methods for substantial sludge treatment. The most frequently used approach for treating sludge to produces methane and reduces sludge is anaerobic treatment. The hydrolysis phase in WAS limits the breakdown of complex macrobiotic compounds. The presence of extracellular polymeric substances (EPS) in biomass prevents the substrate from being hydrolyzed. Enhancing substrate hydrolysis involves removal of EPS preceded by phase separated pretreatment. Hence, a critical assessment of various phase separated pretreatment that has a remarkable effect on the anaerobic digestion process was documented in detail. Moreover, the economic viability and energy requirement of this treatment process was also discussed. Perspectives and recommendations for methane production were also provided to attain effectual sludge management.

Current advances and future outlook on pretreatment techniques to enhance biosolids disintegration and anaerobic digestion: A critical review

Waste activated sludge (biosolids) treatment is intensely a major problem around the globe. Anaerobic treatment is indeed a fundamental and most popular approach to convert organic wastes into bioenergy, which could be used as a carbon-neutral renewable and clean energy thus eradicating pathogens and eliminating odor. Due to the sheer intricate biosolid matrix (such as exopolymeric substances) and rigid cell structure, hydrolysis becomes a rate-limiting phase. Numerous different pretreatment strategies were proposed to hasten this rate-limiting hydrolysis and enhance the productivity of anaerobic digestion. This study discusses an overview of previous scientific advances in pretreatment options for enhancing biogas production. In addition, the limitations addressed along with the effects of inhibitors in biosolids towards biogas production and strategies to overcome discussed. This review elaborated the cost analysis of various pretreatment methods towards the scale-up process. This review abridges the existing research on augmenting AD efficacy by recognizing the associated knowledge gaps and suggesting future research.

Estimation of Sustainable Bioenergy Production from Olive Mill Solid Waste

The disposal of olive wastes and their wastewater is a major problem worldwide. An important recycling chain can be formed through biogas production and energy conversion from olive waste. This study developed an efficient and effective sustainable model for biogas production using anaerobic digestion conditions with the co-digestion of pretreated olive waste. The sample used was hard olive pomace, which was dried in an oven before being crushed to fine particles with a mortar and pestle. The sample was analyzed by a CE-440 Elemental Analyzer, and Fourier Transform Infrared Spectrophotometer (FTIR) analysis was performed using Shimadzu IRTracer-100. Through the analysis, a substantial amount of electrical energy of 769 kWh/t was found to be generated per ton of olive pomace due to the high volatile solid (VS) percentage of organic waste material incorporated during the calculation. Reduced land area for landfilling olive waste was calculated to be 108 m2 per year, whereas the potential to reduce landfill leachate production was evaluated to be 0.32 m3 per year.

Removal of 17α-ethinylestradiol and caffeine from wastewater by UASB-Fenton coupled system

In aquatic systems, some substances considered as endocrine disruptors have been detected, which can be due to their incomplete elimination in wastewater treatment plants (WWTPs) and inadequate disposal of pharmaceuticals. Among these contaminants are 17α-ethinylestradiol (EE2) and caffeine (CAF). Moreover, it has been reported that this kind of contaminants may provoke different adverse effects in many aquatic organisms. Because of that, in the present study, up-flow anaerobic sludge blanket reactors (UASB) coupled with the Fenton process was evaluated for EE2 and CAF removal spiked in wastewater samples. First, the best reaction conditions were established in each process. For UASB reactor, two hydraulic retention times (HRT 8 and 24 h) were evaluated, achieving the highest chemical organic demand (COD) removal (70 %) and drug elimination (84 %-86 %) with HRT 24 h. Subsequently, Fenton process was conducted at pH 3 with different levels of Fe²⁺ (0.05-0.5 mmol/L) and molar ratios Fe²⁺:H₂O₂ (1:1-1:10). Better results were obtained with 0.5 mmol Fe²⁺/L, and 1:10 ratio molar Fe²⁺:H₂O₂. Finally, UASB-Fenton coupled system allowed 80 % of COD decrease, almost complete removal of drugs and the toxicity of samples on Vibrio fischeri was reduced from 73 % to 30 %, demonstrating that this coupled system is a promising and efficient system for pharmaceutical compounds removal from wastewater.

Deciphering the effects of temperature on bio-methane generation through anaerobic digestion

Anaerobic digestion (AD) is a sustainable wastewater treatment technology which facilitates energy, nutrient, and water recovery from organic wastes. The agricultural and industrial wastes are suitable substrates for the AD, as they contain a high level of biodegradable compounds. The aim of this study was to examine the AD of three different concentrations of phenol (100, 200, and 300 mg/L) containing wastewater with and without co-substrate (acetate) at four different temperatures (25, 35, 45, and 55 °C) to produce methane (CH₄)-enriched biogas. It was observed that the chemical oxygen demand (COD) and phenol removal efficiencies of up to 76% and 72%, respectively, were achieved. The CH₄ generation was found higher in anaerobic batch reactors (ABRs) using acetate as co-substrate, with the highest yield of 189.1 μL CH₄ from 500 μL sample injected, obtained using 200 mg/L of phenol at 35 °C. The results revealed that the performance of ABR in terms of degradation efficiency, COD removal, and biogas generation was highest at 35 °C followed by 55, 45, and 25 °C indicating 35 °C to be the optimum temperature for AD of phenolic wastewater with maximum energy recovery. Scanning electron microscopy (SEM) revealed that the morphology of the anaerobic sludge depends greatly on the temperature at which the system is maintained which in turn affects the performance and degradation of toxic contaminants like phenol. It was observed that the anaerobic sludge maintained at 35 °C showed uniform channels leading to higher permeability through enhanced mass transfer to achieve higher degradation rates. However, the denser sludge as in the case of 55 °C showed lesser permeability leading to limited transfer and thus reduced treatment. Quantitative real-time PCR (qPCR) analysis revealed a more noteworthy change in the population of the microbial communities due to temperature than the presence of phenol with the methanogens being the dominating species at 35 °C. The findings suggest that the planned operation of the ABR could be a promising choice for CH₄-enriched biogas and COD removal from phenolic wastewater.

Regulating acidogenesis and methanogenesis for the separated bio-generation of hydrogen and methane from saline-to-hypersaline industrial wastewater

Given the limitations of acidogens and methanogens activities under saline environments, this work aims to optimize the main operational parameters affecting hydrogen and methane production from saline-to-hypersaline wastewater containing mono-ethylene glycol (MEG). MEG is the main contaminant in several saline industrial effluents. Anaerobic baffled reactor (ABR), as a multi-stage system, was used at different temperatures (i.e., 19-31 °C [ambient] and 35 °C), organic loading rates (OLRs) of 0.6-2.2 gCOD/L/d, and salinity of 5-35 gNaCl/L. Mesophilic conditions of 35 °C substantially promoted MEG biodegradability (92-98%) and hydrogen/methane productivity, even at elevated salinity. Hydrogen yield (HY) and methane yield (MY) peaked to 258 and 140 mL/gCOD_add, respectively, at OLR 0.64 gCOD/L/d and salinity up to 20-25 gNaCl/L. An immobilized sludge ABR (ISABR), packed with polyurethane media, was further compared with classical ABR, resulting in 1.8-fold higher MY, at 35 gNaCl/L. Microbial analysis showed that introducing attached growth system (ISABR) substantially promoted methanogens abundance, which was dominated by genus Methanosarcina. Among bacterial genera, Acetobacterium was dominant, particularly in 1^st compartment, representing MEG-degrading/salt-tolerant genus. At high salinity up to 35 gNaCl/L, the multi-phase and attached growth configuration can efficiently reduce the induced salt stress, particularly on methanogens, towards balanced and separated acidogenesis/methanogenesis. Overall, producing hydrogen and methane from anaerobic treatment of MEG-based saline wastewater is feasible at optimized parameters and configuration.

Membrane fouling and performance of anaerobic ceramic membrane bioreactor treating phenol- and quinoline-containing wastewater: granular activated carbon vs polyaluminum chloride

Although anaerobic membrane bioreactor (AnMBR) has been proposed for the treatment of phenolic wastewater, the membrane fouling is still a major obstacle. The effects of dosing of granular activated carbon (GAC) and polyaluminum chloride (PACl) on the treatment performance and membrane fouling of anaerobic ceramic membrane bioreactor were investigated for treating phenol- and quinoline-containing wastewater. The results suggested that the one-off dosing of GAC resulted in a decrease of protein/carbohydrate ratio, which might account for the aggravation of membrane fouling alongside with the decreased flocs size. Nevertheless, the substrate uptake rates (SUR) of phenol and quinoline, and the specific methanogenic activity of sludge at the GAC dosing stage of experimental reactor (R1) were 8.79 ± 0.63 mg phenol g^-1 MLVSS d^-1, 7.01 ± 0.09 mg quinoline g^-1 MLVSS d^-1 and 0.27 ± 0.01 g COD_CH4 g^-1 MLVSS d^-1, which were 1.69, 3.59 and 1.93 times higher than that of the control reactor (R2). The dosing of PACl reduced the membrane fouling rate by changing the floc structure of sludge, as well as the component of SMP and EPS. However, the substrate uptake rate of quinoline was declined. This work provides a comprehensive evaluation on the effect of GAC and PACl dosing on membrane fouling and performance of anaerobic ceramic membrane bioreactor treating phenol-and quinoline-containing wastewater.

Removal of Phenol from Steel Plant Wastewater in Three Dimensional Electrochemical (TDE) Process using CoFe2O4@AC/H2O2

This study investigated the removal of phenol from steel industry wastewater by three dimensional electrochemical (TDE) process using CoFe2O4 nanobiocomposite based activated carbon in the presence of H2O2 (EC-CoFe2O4@AC-H2O2). In this study, CoFe2O4 nanobiocomposite-foundation activated carbon (CoFe2O4@AC) was used as microelectrode, adsorbent, and activator for peroxide hydrogen. The removal efficiency of phenol and COD was investigated through the parameters of pH, contact time, CoFe2O4@AC dosage, current density, and H2O2 concentration. The highest removal rates of phenol and COD were >99% and 98%, respectively. Also, steel plant wastewater under the optimal conditions of pH = 6.5, current density = 15 mA cm−2, contact time = 25 min, H2O2 concentration of 1.0 mM, and CoFe2O4@AC dose = 0.3 g L−1. Kinetic analysis revealed that the adsorption experimental data was best fitted by the pseudo-first-order model.