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Anaerobiosis, Electrolysis, Family Characteristics, Food, Methane, Bioreactors, and Refuse Disposal

This study reveals the efficient treatment of high strength food waste under varying hydraulic retention times (48 h, 36 h and 24 h) in a continuous stirred tank reactor (CSTR) integrated with microbial electrolysis cell (MEC) to become a continuous stirred microbial electrolysis cell (CSMEC). COD removal efficiency in the CSMEC surpassed 92% with OLR ranging from 0.4 to 21.31 kg COD/m 3 ·d compared to that of the CSTR. The maximum current density (based on the cathode surface area) was 1125.35 ± 81 mA/m 2 in the CSMEC. Biogas yield and methane production rates increased by 16.5% and 19.3% in the CSMEC respectively compared to the CSTR. CSMEC was 1.52 times better in performance compared to the CSTR. Firmicutes, Synergistetes, Bacteroidetes, Thermotogae, Chloroflexi and Proteobacteria were the dominant phyla associated with both CSMEC and CSTR. Archaeal microbial community analysis showed Methanosaeta, Methanobacterium, Methanosarcina and Methanocorpusculum as the dominant populations associated with the CSMEC.
(Copyright © 2020 Elsevier B.V. All rights reserved.)

Anaerobiosis, Hydrogen-Ion Concentration, Nitrogen, Oxidation-Reduction, Sewage, Bioreactors, and Waste Disposal, Fluid

In order to assess the performance of anaerobic ammonium oxidation (anammox) bioreactors, it is necessary to study the stoichiometry of the anammox reaction and pH. This study focused on the effect of the hydraulic retention time (HRT) on the effluent pH in anammox-upflow anaerobic sludge blanket (UASB) bioreactors. Anammox-UASB bioreactors with and without a recirculation system were used to investigate the effluent pH and bioreactor performance. It was concluded that under varying HRT conditions, the decrease in effluent pH did not indicate the deterioration of nitrogen removal, but did indicate that the nitrogen removal efficiency was reduced owing to a sudden increase in the nitrogen loading rate resulting from the decrease in HRT. Moreover, the results showed that the HRT directly affected the concentration of OH - , which affected the increase/decrease in effluent pH. This study demonstrated that effluent pH is a more powerful tool than previous techniques used to assess bioreactor performance. We suggest that the effluent pH could be used for preliminary assessment.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Anaerobiosis, Nitrogen, Sewage, Waste Disposal, Fluid, Waste Water, Bioreactors, and Phosphorus

Recovering energy from wastewater in addition to its treatment is a hot trend in the new concept of water resource recovery facility (WRRF). High-rate systems operating at low solid retention time (SRT) have been proposed to meet this challenge. In this paper, the integration of Enhanced Biological Phosphorus Removal (EBPR) in an anaerobic/aerobic continuous high-rate system (A-stage EBPR) was evaluated. Successful P and COD removal were obtained operating at SRT 6, 5 and 4 days treating real wastewater, while a further decrease to 3 days led to biomass washout. The best steady state operational conditions were obtained at SRT = 4d, with high removal percentage of P (94.5%) and COD (96.3%), and without detecting nitrification. COD mineralization could be reduced to 30%, while 64 % of the entering carbon could be diverted as biomass to energy recovery. Regarding nitrogen, about 69±1% of the influent N was left as ammonium in the effluent, with 30% used for biomass growth. The aerobic reactor could be operated at low dissolved oxygen (DO) (0.5 mg/L), which is beneficial to decrease energy requirements. Biochemical methane potential (BMP) tests showed better productivity for the anaerobic sludge than the aerobic sludge, with an optimal BMP of 296±2 mL CH 4 /gVSS. FISH analysis at SRT = 4d revealed a high abundance of Accumulibacter (33±13%) and lower proportion of GAO: Competibacter (3.0±0.3%), Defluviicoccus I (0.6±0.1%) and Defluviicoccus II (4.3±1.1%).
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Bacteria, Extracellular Polymeric Substance Matrix, Sewage, Bioreactors, and Waste Disposal, Fluid

The application of granular biomass has enabled energy efficient, high-rate wastewater treatment systems. While initially designed for high-strength wastewater treatment, granular systems can also play a major role in resource recovery. This study focused on the formation of purple phototrophic bacteria (PPB) granular biomass during synthetic wastewater treatment. Liquid upflow velocity was applied as the driving force for granulation. Separate reactors were operated at either low (2-5m h -1 ) or high (6-9m h -1 ) upflow velocities, with sludge retention times (SRTs) ranging from 5-15d. Reactors produced anaerobic, photo-granules within ~50d. The sludge volume index (SVI 30 ) of the granules was 10mL g -1 and average settling rates were greater than 30m h -1 , both metrics being similar to existing granular technologies. Granule sizes of 2-3mm were recorded, however the particle size distribution was bimodal with a large floc fraction (70-80% volume fraction). The extracellular polymeric substance (EPS) and alginate-like extract (ALE) contents were similar to those in aerobic granular biomass. Fluorescence in-situ hybridisation (FISH) imaging identified PPB bacteria dispersed throughout the granules with very few methanogens and an active core. Outer layer morphology was substantially different in the two reactors. The high-upflow reactor had an outer layer of Chromatiales and an inner layer of Rhodobacteriales, while the low-upflow reactor had lower abundances of both, and limited layering. According to 16s gene sequencing, PPB were a similar fraction of the microbial community in both reactors (40-70%), but the high upflow granules were dominated by Chromatiales (supporting FISH results), while the low upflow velocity reactor had a more diverse PPB community. Methanogens were seen only in the low upflow granules and only in small amounts (≤8%). Granule crude protein content was ~0.60gCP gVS -1 (~0.45gCP gTS -1 ), similar to that from other PPB production technologies. The growth of a rapid settling and discrete PPB granular biomass on synthetic wastewater suggests methods for resource recovery using PPB can be diversified to also include granular biomass.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Biological Oxygen Demand Analysis, Denitrification, Nitrification, Nitrogen analysis, Bioreactors, and Nitrous Oxide analysis

Nitrous oxide (N 2 O) generated from wastewater treatment plants (WWTPs) has drawn attention due to its high emission load and significant greenhouse effect. In the present study, N 2 O emissions from a pilot-scale Carrousel oxidation ditch under various chemical oxygen demand (COD) to nitrogen ratio (COD/N) and aeration rates were systematically investigated. The highest N 2 O emission factor was 0.142 ± 0.013%, at COD/N of 5 and aeration rate of 1.8 m 3  h -1 , which was much lower than the majority of previous studies. The results could be attributed to the high internal recycle ratio of the oxidation ditch process which lightened the burden of influent load to the system. The profiles of N 2 O emissions and dissolved N 2 O concentration along the channels showed a distinct spatial variation that N 2 O emissions primarily occurred in the aeration zones due to the air stripping effect. However, both the aeration and anoxic zones contributed to N 2 O generation due to autotrophic nitrification (AN), which was considered to be the main N 2 O generation process. In addition, two simulated shock-load conditions, ammonia overload shock and aeration failure shock, were carried out to explore the response of the biological nitrogen removal (BNR) system. The results indicated that both shock-loads lead to excessive N 2 O emissions, especially at higher aeration rates, which could be explained by the improved N 2 O generation by AN process during the shock-load period. This study offered new insights into the role of operational parameters to N 2 O emission and the alternative approach for N 2 O mitigation during both the steady-state operation and shock-load conditions in the oxidation ditch process.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Anaerobiosis, Fatty Acids, Methane, Bioreactors, and Water Purification

The inhibition of the anaerobic digestion (AD) process, caused by long chain fatty acids (LCFAs), has been considered as an important issue in the wastewater treatment sector. Proper understanding of mechanisms behind the inhibition is a must for further improvements of the AD process in the presence of LCFAs. Through analyzing recent literature, this review extensively describes the mechanism of LCFAs degradation, during AD. Further, a particular focus was directed to the key parameters which could affect such process. Besides, this review highlights the recent research efforts in mitigating LCFAs-caused inhibition, through the addition of commonly used additives such as cations and natural adsorbents. Specifically, additives such as bentonite, cation-based adsorbents, as well as zeolite and other natural adsorbents for alleviating the LCFAs-induced inhibition are discussed in detail. Further, panoramic evaluations for characteristics, various mechanisms of reaction, merits, limits, recommended doses, and preferred conditions for each of the different additives are provided. Moreover, the potential for increasing the methane production via pretreatment using those additives are discussed. Finally, we provide future horizons for the alternative materials that can be utilized, more efficiently, for both mitigating LCFAs-based inhibition and boosting methane potential in the subsequent digestion of LCFA-related wastes.
(Copyright © 2020. Published by Elsevier Ltd.)

Hydrolysis, Nitrification, Nitrogen, Sewage, Waste Disposal, Fluid, Ammonia, and Bioreactors

The benefits of deammonification to remove nitrogen from sidestreams, i.e., sludge dewatering liquors, in municipal wastewater treatment plants are well accepted. The ammonia removal from dewatering liquors originated from thermal hydrolysis/anaerobic digestion (THP/AD) are deemed challenging. Many different commercial technologies have been applied to remove ammonia from sidestreams, varying in reactor design, biomass growth form and instrumentation and control strategy. Four technologies were tested (a deammonification suspended sludge sequencing batch reactor (S-SBR), a deammonification moving bed biofilm reactor (MEDIA), a deammonification granular sludge sequencing batch reactor (G-SBR), and a nitrification suspended sludge sequencing batch reactor (N-SBR)). All technologies relied on distinct control strategies that actuated on the feed flow leading to a range of different ammonia loading rates. Periods of poor performance were displayed by all technologies and related to imbalances in the chain of deammonification reactions subsequently effecting both load and removal. The S-SBR was most robust, not presenting these imbalances. The S-SBR and G-SBR presented the highest nitrogen removal rates (NRR) of 0.58 and 0.56 kg N m -3  d -1 , respectively. The MEDIA and the N-SBR presented an NRR of 0.17 and 0.07 kg N m -3  d -1 , respectively. This study demonstrated stable ammonia removal from THP/AD dewatering liquors and did not observe toxicity in the nitrogen removal technologies tested. It was identified that instrumentation and control strategy was the main contributor that enabled higher stability and NRR. Overall, this study provides support in selecting a suitable biological nitrogen removal technology for the treatment of sludge dewatering liquors from THP/AD.
(Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

Ammonia, Nitrogen, Oxidation-Reduction, Technology, Waste Water analysis, Ammonium Compounds, and Bioreactors

Deammonification (partial nitritation-anammox) process is a favorable and innovative process, for treatment of nitrogen-rich wastewater due to decreased oxygen and carbon requirements at very high nitrogen loadings. The bacterial groups responsible for this process are anaerobic ammonium oxidation (anammox) bacteria in symbiosis with ammonium oxidizing bacteria (AOB) which have an active role in development of nitrogen removal biotechnology in wastewater. Development and operation of sidestream deammonification processes has augmented since the initial full-scale systems, yet there are several aspects which mandate additional investigation and deliberation by the practitioners, to reach the operating perspective, set for the facility. Process technologies for treatment of streams with high ammonia concentrations continue to emerge, correspondingly, further investigation towards feasibility of applying the deammonification concept, in the mainstream treatment process is required. Mainstream deammonification can potentially improve the process of achieving more sustainable and energy-neutral municipal wastewater treatment, however feasible applications are not accessible yet. This critical review focuses on a comprehensive assessment of the worldwide lab-scale, pilot-scale and full-scale sidestream applications as well as identifying the major issues obstructing the implementation of mainstream processes, in addition to the designs, operational factors and technology advancements at both novel and/or conventional levels. This review aims to provide a novel and broad overview of the status and challenges of both sidestream and mainstream deammonification technologies and installations worldwide to assess the global perspectives on deammonification research in the recent years. The different configurations, crucial factors and overall trends in the development of deammonification research are discussed and conclusively, the future needs for feasible applications are critically reviewed.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Anaerobiosis, Ions, Iron, Methane, Waste Disposal, Fluid, Bioreactors, and Sewage

This study was conducted to investigate the effects of residual ferric ions (FI), released from iron or its oxides for wastewater or waste activated sludge (WAS) treatment, on anaerobic digestion of WAS. Herein it was found that the anaerobic digestion process was greatly affected by FI dosages as well as FI distributions. The responses of performance and microorganism suggested that a low FI (e.g., 0.125 mmol/g volatile suspended solid (VSS)) enhanced methane production by 29.3%, and a medium FI (e.g., 0.3 mmol/g VSS) promoted short chain fatty acids accumulation to reach the maximum of 247 mg chemical oxygen demand /g VSS, conversely, a high FI (e.g., 0.9 mmol/g VSS) led to severe inhibition on acidogenesis and methanogenesis. The findings may provide some new insights for mechanism understanding on anaerobic digestion process influenced by iron or its oxides, as well as the disposal of WAS contained FI.
(Copyright © 2020. Published by Elsevier Ltd.)

Bacteria, Nitrites, Nitrogen, Oxidation-Reduction, Bioreactors, and Sewage

To investigate the effect of sludge ratio on the hybrid CANON system, autotrophic nitrogen removal sludge was inoculated with different granule/floc ratios to initiate the CANON system, and maintained the sludge ratio during the operation process. The start-up performances were compared, and the distribution characteristics of functional bacteria were investigated. The results show that the Equivalent system (granules:flocs = 1:1-1:1.5) successfully started-up on day 19, and the nitrogen removal rate (NRR) reached 0.299 kgN m -3 ·d -1 on day 63. At the same time, it was less affected by the load shock than High-granules and High-flocs systems. Therefore, the Equivalent system had the strongest start-up performance. The activities of the functional bacteria conformed to spatial heterogeneity, unlike the abundance. With the increased floc proportion, the difference in the activity and abundance of anaerobic ammonium-oxidizing bacteria (AAOB) between the granules and flocs increased, while there was a decrease in the difference in aerobic ammonium-oxidizing bacteria (AOB). However, the abundance of Nitrosomonas in the granules was higher than in the flocs when the proportion of flocs was higher than 50%. This study provides new ideas and insights for the fast start-up of the CANON system and can conform to the varying needs of engineering applications.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Anaerobiosis, Biofuels, Methane, Bioreactors, and Sewage

Anaerobic digestion is the preferred method for treating sewage sludge because of its ability to reduce sludge volume and produce biogas. However, conventional anaerobic digestion has a long retention time and low degradation rate. In recent years, hydrothermal treatment has been used to improve the hydrolysis of sewage sludge and biogas production. This process tends to focus on maximizing biogas production. However, very little research has been done on anaerobic digestion residues. In this study, batch experiments were conducted to investigate the effect of hydrothermal temperature on methane production and the contents of liquid fraction after anaerobic digestion (centrate). Experimental conditions were designed using a response surface method and central composite model. A quadratic equation was used to interpret the individual and interactive effects of hydrothermal conditions on anaerobic digestion. Given the maximum biogas production and the minimum concentrate concentration, the optimal operating condition was determined by a 186 °C hydrothermal temperature and a reaction time of 106 min. Under these conditions, the following results could be obtained: methane production (200.5 ± 7.7 mL-CH 4 /gVS added ), TCOD (16,572 ± 348 mg/L), sCOD (1240 ± 65 mg/L), sTN (658.9 ± 8.0 mg/L) and ammonia (525 ± 27 mg/L).
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Anaerobiosis, Biofuels, Methane, Bioreactors, and Oryza

This study investigated the anaerobic bioconversion efficiency of rice straw in continuously stirred tank reactor (CSTR) applying longer hydraulic retention time (HRT) and higher load. Two HRT distributions and two loads were studied and compared for one-stage and two-stage CSTR systems. The results indicated that the two system with longer HRT (60d) and higher load (160g TS·L -1 ) obtained 11.06% and 14.28%, 15.24% and 19.38%, more biogas and methane productions than those of one-stage system with HRT (50d) and load (140g TS·L -1 ), respectively, while maintained stable operation at higher loads. It was also found that the microbial richness, diversity, and bacterial and archaeal community compositions showed some differences between two systems with different HRTs and loads, which was thought to be one of reasons leading to the differences in bioconversion efficiencies. The study indicated that two-stage system applying longer HRT and higher load could be one of the effective methods for more bioenergy recovery from rice straw.
(Copyright © 2020. Published by Elsevier Ltd.)

Anaerobiosis, Biofuels, Fermentation, Hot Temperature, Bioreactors, and Methane

An outdoor anaerobic fermentation reactor loses a significant amount of energy due to heat dissipation to the surrounding environment. The digester of direct absorption biogas can effectively utilize solar energy and scattering of the medium to enhance reaction temperature, which can promote anaerobic fermentation of microorganisms. A numerical model for the direct absorption methane digester was established to investigate the mechanism of photo biochemical transformation. The average relative values of simulated results were 4.1% and 9.6%, indicating that the model can effectively simulate the heat transfer process of biogas slurry under solar irradiation. Decreasing the albedo and increasing the effect of forward scattering of small particles can improve the regenerative performance and biogas production of digester. Increasing the backward scattering effect of small particles limited biogas fermentation. Scattering distribution had bigger effects on the rates of biogas and propionic acid production than those of albedo.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Nitrogen, Oxidation-Reduction, Sewage, Biofilms, and Bioreactors

The effects of aeration regimes (intermittent and continuous aeration) on nitritation performance and biofilm EPS composition were evaluated in moving bed biofilm reactors (MBBRs), and a hypothesis that the aeration regimes affect EPS composition by affecting the microbial activity and sludge discharge content was proposed. The effluent NO 2 - /NH 4 + ratio corresponded to that of an anammox reaction (1.07 ± 0.20) for the MBBR with continuous aeration (MBBR con. ), while that in the MBBR with intermittent aeration (20 min on/15 min off) (MBBR int. ) was relatively lower (0.75 ± 0.19). Furthermore, the activity of ammonia-oxidizing bacteria in MBBR con. was 0.4-7.9 mg-N·L -1 ·h -1 more than that in MBBR int. , which was consistent with the lower proportion of dead cells in MBBR con. compared with MBBR int. (9.4% vs. 31.8%). The higher microbial activity in MBBR con. led to more sludge discharge than MBBR int. , which was reflected in the higher biofilm detachment rate in MBBR con. compared with MBBR int. (0.15 ± 0.02 vs. 0.11 ± 0.02 g m -2 ·d -1 ). The ratio of humic substances to polysaccharides in the EPS was high (0.96 ± 0.08) in the detachment biomass, while the ratios in the nitritation biofilm on carriers from MBBR con. and MBBR int. were 0.52 ± 0.13 and 0.72 ± 0.16, respectively. We hypothesized that biofilm matrix with high ratios of humic substances to polysaccharides are structurally unstable and prone to fall off. In addition, the higher proportion of dead cells in MBBR int. made the proportion of humic substances in EPS high. Meanwhile, less sludge discharge in MBBR int. than MBBR con. caused more humic substances to accumulate in the biofilm. These was responsible for the higher ratio of humic substances to polysaccharides in MBBR int. compared with MBBR con . The findings elucidate the connection between aeration regimes and biofilm EPS composition, and guide the choice of aeration regimes in the design of biofilm reactors for partial nitritation.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Anaerobiosis, Food, Hydrogen-Ion Concentration, Methane, Bioreactors, and Refuse Disposal

This study investigated responses of anaerobic digestion (AD) of food waste (FW) with different inocula to varying organic loads and to pH control under high load in terms of process performance and microbial characteristics. Without pH control, digester inoculated by thickened sludge obtained high methane yield of 547.8 ± 27.8 mL/g VS under organic load of 7.5 g VS/L but was inhibited by volatile fatty acids (VFAs) under higher loads (15 and 30 g VS/L). However, digesters inoculated by anaerobic sludge obtained high methane yields of 575.9 ± 34.2, 569.3 ± 24.8 and 531.9 ± 26.2 mL/g VS under organic loads of 7.5, 15 and 30 g VS/L and VFAs inhibition only appeared under extremely high load of 45 g VS/L. Digesters under VFA inhibition with high load were significantly enhanced by controlling single ecological factor pH at 6.5, 7.0 and 7.5, as indicated by shorter lag phases, higher peak values of methane production rate, greater methane yields and fast VFAs degradation. Maximum methane recovery was obtained with pH control at 7.5 under high load. VFA inhibition was accompanied by the degeneration of ecological functions of Syntrophomonadaceae and unidentified Bacteroidales and the dominant growth of unidentified Clostridiales. Under high load and pH control, high stability was strongly associated with obvious growth of Methanosarcina, which enriched methanogenic pathways thus improved system robustness and tolerance to VFAs. Moreover, pH control stimulated the growth of syntrophic Bacteria Syntrophomonadaceae while maintaining the high activity of hydrogenotrophic methanogens therefore sustained efficient syntrophic communities of Bacteria and methanogens and avoided over accumulation of VFAs. pH control promoted adaptive selection of methanogens, leading to obvious decline of archaeal community diversity. This study provided practical guidance on digester configurations of high-load AD of FW and expanded the understanding of responses to coupling effects of inoculum origins, organic loads and pH control under high load concerning process performance and microbial community dynamics.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Heterotrophic Processes, Nitrates, Nitrification, Nitrogen, Bioreactors, and Denitrification

This study aimed to explore how dissolved oxygen (DO) affected the characteristics and mechanisms of denitrification in mixed bacterial consortia. We analyzed denitrification efficiency, intracellular nicotinamide adenine dinucleotide (NADH), relative expression of functional genes, and potential co-occurrence network of microorganisms. Results showed that the total nitrogen (TN) removal rates at different aeration intensities (0.00, 0.25, 0.63, and 1.25 L/(L·min)) were 0.93, 1.45, 0.86, and 0.53 mg/(L·min), respectively, which were higher than previously reported values for pure culture. The optimal aeration intensity was 0.25 L/(L·min), at which the maximum NADH accumulation rate and highest relative abundance of napA, nirK, and nosZ were achieved. With increased aeration intensity, the amount of electron flux to nitrate decreased and nitrate assimilation increased. On one hand, nitrate reduction was primarily inhibited by oxygen through competition for electron donors of a certain single strain. On the other hand, oxygen was consumed rapidly by bacteria by stimulating carbon metabolism to create an optimal denitrification niche for denitrifying microorganisms. Denitrification was performed via inter-genus cooperation (competitive interactions and symbiotic relationships) between keystone taxa (Azoarcus, Paracoccus, Thauera, Stappia, and Pseudomonas) and other heterotrophic bacteria (OHB) in aeration reactors. However, in the non-aeration case, which was primarily carried out based on intra-genus syntrophy within genus Propionivibrio, the co-occurrence network constructed the optimal niche contributing to the high TN removal efficiency. Overall, this study enhanced our knowledge about the molecular ecological mechanisms of aerobic denitrification in mixed bacterial consortia and has theoretical guiding significance for further practical application.
(Copyright © 2020 Elsevier B.V. All rights reserved.)

Biofilms, Hydrogen, Bioreactors, and Methane

Biomethanation of CO 2 has been proven to be a feasible way to produce methane with the employment of H 2 as electron source. Subject of the present study is a custom-made membrane biofilm reactor for hydrogenotrophic methanation by archaeal biofilms cultivated on membrane surfaces. Reactor layout was adapted to allow for in situ biofilm analysis via optical coherence tomography. At a feeding ratio of H 2 /CO 2 of 3.6, and despite the low membrane surface to reactor volume ratio of 57.9 m 2 m -3 , the maximum methane production per reactor volume reached up to 1.17 Nm 3 m -3 d -1 at a methane content of the produced gas above 97% (v/v). These results demonstrate that the concept of membrane bound biofilms enables improved mass transfer by delivering substrate gases directly to the biofilm, thus, rendering the bottleneck of low solubility of hydrogen in water less drastic.
(Copyright © 2020. Published by Elsevier Ltd.)

Biomass, Fermentation, Food, Bioreactors, and Lactic Acid

Biowaste valorization into lactic acid (LA) by treatment with indigenous microbiota has recently gained considerable attention. LA production from date pulp waste provides an opportunity for resource recovery, reduces environmental issues, and possibly turns biomass into wealth. This study aimed to compare the performance of batch and cyclic fermentation processes in LA production with and without enzymatic pretreatment. The fermentation studies were conducted in the absence of an external inoculum source (relying on indigenous microbiota) and without the addition of nutrients. The highest LA volumetric productivity (3.56 g/liter/day), yield (0.07 g/g-TS), and concentration (21.66 g/L) were attained with enzymatic pretreated date pulp in the cyclic-mode fermentation at the optimized conditions. The productivity rate of LA was enhanced in the cyclic-mode as compared to the batch process. Enzymatic pretreatment increased the digestibility of cellulose that led to higher LA yield. An Artificial Neural Network model was developed to optimize the process parameters and to predict the LA concentration from date pulp waste in both fermentation processes. The main advantage of the ANN approach is the ability to perform quick predictions without resource-consuming experiments. The model predicted optimal conditions well and demonstrated good agreement between experimental and predicted data.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Anaerobiosis, Cooking, Digestion, Methane, Bioreactors, and Sewage

Anaerobic digestion is a promising way for resource recovery from waste cooking oil (WCO) due to its high bio-methanation potential. In-situ mild alkaline (pH 8) enhanced two-stage continuous stirred tank reactors (ALK-2-CSTRs) were implemented to explore its efficiency in co-digesting WCO and sewage sludge with stepwise increase of WCO in the co-substrates. Results demonstrate that the ALK-2-CSTRs effectively promoted methane yield from the co-substrates via promoting hydrolysis, long chain fatty acids (LCFAs) degradation and protecting methanogens from exposure to high concentration of LCFAs directly. The maximum methane yield of the ALK-2-CSTRs is 39.2% higher than that of a single stage CSTR system at the optimal feed mixture of 45:55 (WCO:SS [VS]). The thermophilic operation applied to the stage-1 of the ALK-2-CSTRs failed to improve the methane yield when the methanogenic performance was stable; while upon WCO overloaded, the elevated temperature mitigated the deterioration of methanogenesis by stimulating the bioconversion of the toxic LCFAs, especially the unsaturated oleic acid. Microbial community analysis reveals the ALK-2-CSTRs stimulated the growth of lipolytic bacteria and hydrogenotrophic methanogens, which suggests the hydrogenotrophic methanogenic pathway was promoted. Cost evaluation demonstrates the economical superiority of the ALK-2-CSTR over the prevailing strategies developed for enhancing methane yield from the co-substrates.
(Copyright © 2020 Elsevier Ltd. All rights reserved.)

Anaerobiosis, Biological Oxygen Demand Analysis, Hydrolysis, Temperature, Volatilization, Waste Disposal, Fluid, Bioreactors, and Sewage

Autohydrolysis or enzyme hydrolysis pretreatment under thermophilic conditions significantly accelerates organic solubilization of waste activated sludge (WAS), allowing enhanced methanogenesis in subsequent mesophilic anaerobic digestion. Solubilization mechanisms can hardly be explained and clarified using only conventional analytical measurements, such as soluble chemical oxygen demand (COD) and volatile suspended solids (VSS). Here, we proposed a new but readily available analytical method where volatile solids (VS) are fractionized into high volatile solids (VS 205 ), moderate volatile solids (VS 350 ), and low volatile solids (VS 505 ). In a laboratory-scale experiment, anaerobic digesters were operated at 55, 65, and 75°C with thickened WAS. The high volatile solids (VS 205 ) sensitively reflected the temperature effect while the low volatility solids (VS 505 ) showed relatively insensitive results to the examined temperature conditions. This finding indicates that hydrolysis of high volatile solids (VS 205 ) was accelerated more effectively with the increased temperature. Also, based on the experimental results with the fractionized volatile solids, we recommend that autohydrolysis pretreatment should be operated at 75°C for 5 hr to achieve both rapid hydrolysis and reduced energy consumption. PRACTITIONER POINTS: The volatile solids (VS) were divided into high volatile, moderate volatile, and low volatile fractions. The fractionated VS showed how organic solids were hydrolyzed in thermophilic pretreatment of thickened waste activated sludge. At the higher temperature (75°C), the high volatile fraction increased substantially compared to 55 or 65°C. The fractionated VS responded more sensitively to the thermophilic temperatures compared to common analysis parameters (COD, VSS). We recommend thermophilic pretreatment at 75°C for 5 hr for thickened waste activated sludge.
(© 2020 Water Environment Federation.)