Semi-continuous Experiments Research Articles

Simplified Modeling of High-Solids Anaerobic Digestion of Dairy Manure in a Pilot-Scale Stirred Tank Anaerobic Digester

Highlights HSAD is a cost-effective approach for managing high-solids manure. Batch digestion of HSAD at a low inoculum ratio is unsuitable. Mixing once a day was enough to maintain a stable digestion process. The stoichiometric method with an appropriate biodegradability factor provided perfect prediction. Simplified biokinetics can predict methane productivity at steady-state conditions. Abstract. Anaerobic digestion (AD) is considered one of the most effective methods of managing dairy manure. To effectively and economically treat the huge volumes of manure produced by commercial dairy farms, high-solids anaerobic digestion (HSAD) is to be encouraged. In this manuscript, batch and semi-continuous anaerobic digestion experiments of dairy manure with a high volatile solid (VS) content were conducted in a pilot-scale stirred digester with an effective volume of 1.63 m3, operated under mesophilic temperature conditions. Three intermittent mixing treatments (50, 100, and 150 rpm) were mixed once a day during feeding with a constant mixing duration of 5 minutes, including a non-mixed experiment, operating at a 30-day hydraulic retention time. The objectives were to determine an optimum mixing intensity to enhance HSAD efficiency and economy and to apply simplified models to model the digestion process. The simplified kinetic models were modified to accurately predict methane growth, yield, and production rates. The modified Gompertz growth model predicted the methane growth at the batch experiment perfectly. The first-order kinetic model predictions of the biodegradability factor, the specific methane yield, and the specific methane production rate were consistent with the batch experimental results. The stoichiometric method and the Karim model were modified to accurately model the effect of mixing intensity on the methane yield and the specific methane production rate. Three linear equations were successfully developed to predict the methane production rate. Optimized mixing intensity and organic loading rate are critical for high methane production rates. This study contributes to the ongoing research to improve the efficiency of HSAD. Keywords: Dairy manure, High-solids anaerobic digestion, Methane productivity, Mixing intensity.

Recovering and reuse of textile dyes from dyebath effluent using surfactant driven forward osmosis to achieve zero hazardous chemical discharge

This experimental study explores the feasibility of the reuse of dyes recovered from denim and polyester dyebath effluents using forward osmosis (FO) system to achieve zero hazardous material discharge. In batch experiments, the sodium dodecyl sulfate (SDS) at 0.5 M concentration generated an average flux of 3.5 L/m2/h (LMH) and reverse salt flux (RSF) of only 0.012 g/m2/h (GMH), while maintaining 100% dye rejection. This flux stability comes from the property of surfactants to form micelles and exert a stable osmotic pressure (π) above their critical micelle concentration (CMC). The low RSF is due to the greater micelle size. A colored fouling layer was formed on the membrane active layer (AL), which was easily removed using sodium hydroxide (NaOH) and citric acid. According to Fourier transform infrared spectra and atomic forces microscopy images of the AL, the interaction between foulants and membrane active groups did not significantly affect the physiochemical properties of the membrane. In the semi-continuous experiment, a very stable average flux of 7.3 LMH and RSF of 0.03 GMH was obtained using 0.75 M SDS as draw solution. The stacked 1D proton nuclear magnetic resonance analysis (1HNMR) spectra of both original and recovered disperse dyes showed 100% similarity, which validates the concept that the recovered dyes maintained their integrity during reconcentration and can be reused in the next batch dyeing process. Importantly, the diluted SDS concentration can be directly reused within the same textile industry in scouring and finishing processes. The processes of dye recovery and reuse developed in this study do not produce any waste or hazardous by-products and are suitable for scale-up and onsite industrial applications.

Evaluation of digestate-derived biochar to alleviate ammonia inhibition during long-term anaerobic digestion of food waste

The feasibility of using food waste anaerobic digestate-derived biochar (FWDB) to mitigate ammonia toxicity in an anaerobic digester was evaluated. The optimal conditions for preparing and adding the activated FWDB were explored using response surface experiments, and the long-term effects of adding activated FWDB on digester performance under optimum conditions were verified in semi-continuous experiments. The results showed that the optimal preparation and addition conditions for activated FWDB were pyrolysis temperature of 565 °C, particle size of 0–0.30 mm, and dosage of 15.52 g·L−1. During the long-term operation of the digesters, when the total ammonia nitrogen (TAN) concentration was higher than 2000 mg·L−1, the control and experimental digesters showed deteriorated reactor performance. Volatile fatty acids in the control digester accumulated to 20,306 mg·L−1 after the TAN concentration increased to 3391 mg·L−1, the methane yield decreased to 31 mL·g VS−1, and the digester experienced process failure. In contrast, the experimental digester with added activated FWDB only suffered a slight short-term accumulation of acetate and a slight decline in methane yield. This may be attributed to the adsorption of NH4+/NH3 by activated FWDB, which reduced the TAN concentration in the anaerobic digestion (AD) system and mitigated ammonia toxicity. Microbial analysis and metagenome predictions demonstrated that the community richness, diversity, and evenness, as well as the abundance of acetogens and related key genes (ACSM1, paaF, and acdA) were higher in the experimental digester than in the control digester. This study provides a closed-loop AD enhancement strategy by pyrolysis of digestate and in-situ supplementation into the digester.

Production of medium chain fatty acids through co-fermentation of food waste and sewage sludge without external electron donors

Effective biowaste treatment with renewable bioenergy production has become attractive. In this study, chain-elongation (CE) technology was applied to convert food waste (FW) and sewage sludge (SS) into high value-added medium chain fatty acids (MCFAs) by co-fermentation, which not only reduces environmental pollution but also recovers valuable resources. Five groups of batch co-fermentation experiments were performed using FW and SS at different ratios (FW/SS based on chemical oxygen demand, COD) without external electron donors (EDs) to investigate the effects of different FW/SS ratios on the production of MCFAs. The results showed that 100 % FW (FW/SS=1:0) achieved the highest n-caproate concentration (396.37 ± 35.98 mg COD/L), followed by 75 % FW (FW/SS=3:1) (384.42 ± 28.00 mg COD/L). Moreover, 75 % FW (FW/SS=3:1) had higher n-caproate specificity (11.22 ± 3.81 %) than 100 % FW (7.52 ± 0.68 %). Thus, a semi-continuous co-fermentation experiment at a FW/SS ratio of 3:1 was performed for 90 days to explore the feasibility of long-term MCFAs production without external EDs. The results showed that the maximum MCFAs concentration, specificity, and production rate were 10441.31 mg COD/L, 58.20 %, and 250.59 mg COD/L·d−1, respectively. Among the three MCFAs, n-caproate was the most abundant, accounting for 60.28 %. Microbial community analysis revealed that four lactate-producing bacteria (Bifidobacterium, Olsenella, Atopobium, and Proteiniphilum) co-occurred with Caproiciproducens, developing a CE system driven by lactate as the ED. This study provides new insights into the recovery of resources from FW and SS.

Long-term evaluation of the anaerobic co-digestion of food waste and landfill leachate to alleviate ammonia inhibition

To evaluate the feasibility of the co-digestion of food waste (FW) and landfill leachate (LL) to alleviate ammonia inhibition, a series of batch co-digestion experiments were conducted to explore the optimal substrate mixing ratio, and semi-continuous experiments were conducted to evaluate the long-tern effects of LL addition on methane generation and digestate characteristics of the anaerobic co-digestion system under ammonia stress. The optimum methane generation and digestate properties were observed when the concentration of LL in the dilution liquid in the co-digestion reactor was 40 % (v/v). Significant volatile fatty acid accumulation and lower methane yields were both observed during the long-term FW mono-digestion when the total ammonia nitrogen (TAN) concentration reached 3391.27 mg·L–1. However, stable methane generation was observed in the co-digestion system, even when the TAN was 3721.59 mg·L–1, confirming that the LL alleviated the ammonia inhibition of the FW-based anaerobic digestion (AD) system. Microbial analysis of the AD reactors demonstrated that the relative abundance of Pelotomaculum was higher in the co-digestion system than in the mono-digestion system. Analysis of the phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) confirmed the enrichment of genes involved in butyrate, propionate, and methane metabolism in the co-digestion system. In addition, analysis of the digestate characteristics (i.e., dewaterability, germination index, and heavy metals concentrations) indicated that there was no ecological risk for utilization of the digestate after long-term co-digestion operation. These results aim to provide guidance for using LL to promote the processing of FW in the future.

Effects of seasonal and local co-feedstocks on the performance of continuous anaerobic digestion of cattle slurry

The study's aim was to assess the robustness of farm-type anaerobic digestion with cattle slurry as the main feedstock under the change of co-feedstock type and quality. Fish biomass, rainbow trout offal, potato, and reindeer offal were investigated as possible co-feedstocks in a 428-day semi-continuous reactor experiment. Using fish biomass or rainbow trout offal as co-feedstock (19 % of VS of the feed) produced an average of 220 and 305 L CH4/kg VS compared to the 201 L CH4/kg VS for the manure control. For other co-feedstocks, the differences were not statistically significant. Despite recommendations to acclimate biogas process to new feedstocks with caution, no disturbances in the biogas process were observed, even with sudden changes in co-feedstocks. The use of locally available and seasonal co-feedstocks improved the agronomic quality of the digestates and could be important in securing farms' supply of and self-sufficiency in both energy and fertilizers.

The effects of digestate pyrolysis liquid on the thermophilic anaerobic digestion of sewage sludge — Perspective for a centralized biogas plant using thermal hydrolysis pretreatment

The use of pyrolysis process to valorize digestate from anaerobic digestion (AD) of municipal sewage sludge for biochar production was piloted in a central biogas plant. The pyrolysis also generates pyrolysis liquid with high organics and nutrient contents that currently has no value and requires treatment, which could potentially be done in AD. As the pyrolysis liquid may contain inhibitory compounds, we investigated the effects of adding the pyrolysis liquid on AD of sewage sludge and thermal hydrolysis pretreated sewage sludge (THSS) simulating the full-scale centralized biogas plant conditions. In batch assays, the pyrolysis liquid as such did not produce any methane, and the 1% and 5% (v/w) shares suppressed the methane production from THSS by 14–19%, while a smaller decrease in methane production was observed with sewage sludge. However, in the semi-continuous reactor experiments, pyrolysis liquid at a 1% (v/w) share was added in sewage sludge or THSS feed without affecting the methane yields or digestate characteristics. The laboratory results indicated that pyrolysis liquid can be treated in AD, while extrapolating the results to the centralized biogas plant indicated minor increase in the overall methane production and an increased potential for ammonium recovery.

Anaerobic co-digestion of paper sludge: Feasibility of additional methane generation in mechanical–biological treatment plants

In this work, the feasibility of the anaerobic digestion of paper sludge as a co-substrate in anaerobic digestion mechanical–biological treatment (MBT) plants is investigated. In the first phase, the biochemical properties, biomethane potential (BMP), and pollutant contents of 20 different industrial paper sludges are determined. Following the general evaluation in the BMP tests, the second phase of the project involves the semi-continuous co-digestion of six paper sludges in continuous stirred reactors (CSTR). Paper sludges are categorized according to their origin within the pulp and paper mills: Deinking Sludge (DS), Primary Sludge (PS) and Biological Sludge (BS). The analysis of potentially inhibiting elements shows that the concentrations of chlororganic compounds, mineral oil and some heavy metals are highest in DS, while the mean heavy metal loads in all paper sludges are relatively low compared to other industrial sludges. Large differences in total solids (TS) and volatile solids (VS) contents are observed among the different paper sludges investigated, with DS having the highest TS due to the high inorganic contents. The BMP of the investigated sludges ranges from 90 to 355 NL CH4 kg−1 VS. In subsequent semi-continuous co-digestion experiments simulating MBT conditions, three DS and two fiber sludges (a mixture of PS and BS) show good methane generation rates, while one fiber sludge causes inhibition and indicates an increase in viscosity. In general, co-digestion of paper sludge in anaerobic digestion MBT plants can be a viable option for energy production and also facilitates a safe disposal of the paper sludge digestates.

Heterogeneous Fenton catalyst based on clay decorated with nano-sized amorphous iron oxides prevents oxidant scavenging through surface complexation

• Crystalline and amorphous Fe-oxide-clay composites were compared as Fenton catalysts. • Nano-sized amorphous iron-oxide-clay best-promoted phenanthrene oxidation. • A stable H 2 O 2 complex was formed with the amorphous iron-oxide-clay surface. • Single oxygen was primarily responsible for phenanthrene degradation. • Oxidation of phenanthrene was achieved with minimal H 2 O 2 waste. Heterogeneous Fenton catalysts based on iron-oxides are of great interest due to their low cost and high reactivity. Herein, the activity of nano-sized amorphous iron-oxide particles deposited on montmorillonite clay (MMT) was compared to crystalline hematite and magnetite-coated MMT. Hematite, magnetite, and their respective clay composites showed little catalytic activity and almost no phenanthrene (PHE) oxidation at circumneutral pH - in part, due to the decomposition of hydrogen peroxide. In contrast, the amorphous iron oxide (Fe)-MMT, showed very high catalytic activity (over 60% PHE degradation in 60 min) with only minimal consumption of H 2 O 2 (3.3%). In-depth characterization of the Fe-MMT coupled with kinetic and mechanistic experiments was performed to understand the reaction pathway and mechanism. The results suggest that initially H 2 O 2 is complexed to the nano-sized iron oxide catalytic sites on the surface, forming a stable Fe-MMT-H 2 O 2 complex that is activated primarily when the pollutant is introduced. The reactive species, ∙OH and 1 O 2 , were detected upon the diffusion of PHE to the surface - leading to oxidation and mineralization with a minimal decomposition of H 2 O 2 . Quenching experiments further revealed that 1 O 2 played an important role in the extensive mineralization of PHE. The amorphous Fe-MMT also exhibited high stability and performance in semi-continuous cycle batch experiments. Thus, this low-cost and simple Fe-MMT catalyst was found to be highly efficient towards the activation of H 2 O 2 , oxidizing PHE rapidly while reducing radical scavenging and unwanted side reactions. These findings, regarding the role of amorphous phases in the reactivity of iron-oxides, have the potential to improve the design and implementation of solid Fenton catalysts for pollutant remediation in engineered and natural systems.

Effect of organic load regulation on anaerobic digestion performance and microbial community of solar-assisted system of food waste

Abstract The semi-continuous digestion experiment of food waste was carried out based on a solar-assisted heat anaerobic digestion reactor. The effects of organic load regulation (OLR of 2.0, 4.0, 6.0 and 7.0 kg m−3 d−1 VS (volatile solid)) on methane production, physical and chemical parameters, and microbial community structure were studied. The results showed that 6.0 kg m−3 d−1 VS could achieve the optimal methane production as the anaerobic digestion limit OLR of kitchen waste. At this stage, the accumulation of organic acids in the reactor led to a great fluctuation of pH. Artificial alkali regulation could restore the stable operation of the reactor, but the reactor could not withstand the OLR shock of 7.0 kg m−3 d−1 VS. In addition, Qualcomm sequencing results showed that microorganisms showed high functional concentration and poor community richness under low OLR, and increasing OLR could promote microbial richness. At the same time, the Methanosaeta of acetic acid methanogens was relatively abundant in the low OLR stage, while the hydrogen trophic methanogenic bacteria Methanoregula and Methanospirillum showed high activity in the high OLR stage, but the excessive reproduction of acidogenic bacteria in the digestive system would affect the stability of the archaea community when the OLR was too high.

Simultaneous supplementation of magnetite and polyurethane foam carrier can reach a Pareto-optimal point to alleviate ammonia inhibition during anaerobic digestion

Material addition is a potential method to alleviate ammonia inhibition in the anaerobic digestion process. In this study, seven materials were selected to examine their impact on methane production (MP). In the batch experiment, the reactors with “Magnetite + foam carrier” exhibited nearly a 56% increase in maximum MP rate. Different strategies of magnetite and foam carrier addition were further explored in semi-continuous experiment. Adding two materials together (simultaneous supplementation) resulted in almost 60% increase in MP, 28–41% higher than when supplemented separately. Simultaneous supplementation of the two materials was considered as the Pareto-optimal solution for MP maximization. The acetogenic and methanogenic activities analyses revealed that foam carrier addition accelerated propionate transformation (from propionate to acetate or valerate) while magnetite addition intensified the methanogenesis step. Direct interspecies electron transfer (DIET) was strengthened with over 50% enrichment in DIET-related bacteria. The Anaerobic Digestion Model No.1 was modified with the development of liquid metabolite and biofilm, result in a goodness-of-fit of R2 > 0.96.16sRNA gene sequencing demonstrated that the microbes in the biofilm had kinetic advantages over those in the liquid phase, coupled with higher km and lower Ks values, which contributed to the enhanced MP.

Batch and semi–continuous experiments examining the sludge mesophilic anaerobic digestive performance with different varieties of rice straw

Anaerobic co–digestion of excess sludge (ES) and different varieties of rice straw including indica rice straw (IRS), japonica rice straw (JRS) and glutinous rice straw (GRS) was investigated in batch and semi–continuous experiments. The batch experiment results showed that the GRS addition presents the highest hydrolysis and methanogenesis rates, its cumulative methane yield (CMY) was 305.75 mL/g VS and its average methane content was 60.56%. After digestion, the structure of GRS was almost completely destroyed, which was beneficial to the degradation of lignocellulose. The digestive process is affected by the abundance of Actinobactereria, Proteobacteria, Methanosaetae and Methanosarcina. The results of semi–continuous digestion were similar to batch digestion. In addition, the addition of GRS increased TN concentration in biogas residue and TP concentration in biogas slurry, but was not conducive to the subsequent dehydration of sludge.

Green recovery of vanadium from vanadium-bearing shale under the biological action by Bacillus mucilaginosus and its effect on mineral dissolution

The recovery and utilization of vanadium from vanadium-bearing shale is significant, because vanadium is an important strategic metal. In this study, the method for extracting vanadium by Bacillus mucilaginosus was proposed to realize the green recovery of vanadium in vanadium-bearing shale. The optimal conditions for the recovery of vanadium and the phase transformation of vanadium-bearing shale under biological action were investigated. The results showed that the leaching efficiency of vanadium reached 54.2% after 30 days of bioleaching under the optimal conditions of 1 g/L yeast dip powder, which was 33.3% higher than that of the blank group. It was found by FTIR that metabolites such as EPS could adhere to the mineral surface and was gradually consumed over time. The semi-continuous experiment improved the metabolic activity of bacteria, and the released EPS further enhanced the bioleaching effect, in which the leaching efficiency of vanadium increased to 59.1% at 30 days and 61.7% at 50 days. The combined action of bacteria and metabolites removed the hydroxyl group of vanadium-bearing muscovite, further destroyed the basic structure of silicon-oxygen tetrahedron and aluminum oxygen octahedron, resulting in the release of vanadium from the crystal lattice. The recovery of vanadium under biological action could serve as a technical reserve for the green utilization of vanadium-bearing shale in the future.

Possibility of using waste edible oil for biogas production

Anaerobic digestion is a process by which energy from organically degradable waste can be recovered in the form of biogas. The uncontrolled disposal of such organic waste is very burdensome to the environment. In Slovenia, large quantities of waste edible oils are produced every year, which could be used for biogas production. In this study, we investigated the methane potential of waste edible oil in a batch reactor. Further in the pilot scale in a semi-continuous experiment we evaluated the use of waste edible oil in anaerobic digesters of wastewater treatment plant. The results show that the quantity of oil per day that is fed into the anaerobic reactor is limited due to the process's instability and lower biogas production. The optimal daily organic loading of waste edible oil was between 1.6 and 2.4 g VS/L inoculum. During these conditions, the process of anaerobic digestion was stable and methane production was highest. At higher organic loading, the process became unstable, pH was reduced, volatile fatty acids increased, COD at the outflow of reactor increased, and biogas production was significantly reduced.

Effects of substrate organic composition on mesophilic and thermophilic anaerobic co-digestion of food waste and paper waste

Facing the huge output of food waste (FW) and paper waste (PW), long-term semi-continuous experiments were carried out to investigate the effect of the substrate organic composition on mesophilic and thermophilic anaerobic co-digestions (Co-ADs) of their mixtures. The experimental results showed that the organic composition of the substrate affected the biogas and methane production and yield of the two Co-ADs of the FW and PW mixtures, and its effect on thermophilic Co-AD (Co-TAD) was lower than that on mesophilic Co-AD (Co-MAD). The two Co-ADs had similar biogas (2.158 ± 0.136 L/L/d and 2.183 ± 0.142 L/L/d) and methane production (1.245 ± 0.082 L/L/d and 1.279 ± 0.088 L/L/d), and organic matter degradation (81.79 ± 1.07% and 83.81 ± 1.09%) when the substrate organic composition was carbohydrates:proteins:lipids = 6.8:1.8:1 (low carbohydrate composition, FW:PW = 4:1). When the substrate organic composition was carbohydrates:proteins:lipids = 13.5:2:1 (high carbohydrate composition, FW:PW = 1:1), the thermophilic temperature was more favorable than the mesophilic temperature for the Co-AD of FW and PW mixtures. The characteristics (pH, total ammonia, total volatile fatty acids, and total alkalinity) of the Co-TAD digestate were more sensitive to changes in the organic composition of the substrate than those of the Co-MAD digestate. Increasing the carbohydrate content of the FW:PW mixture lowered the production of biogas and methane, and degradation of organic matter in both Co-ADs.

Enzymatic Pretreatment of Byproducts from Soapstock Splitting and Glycerol Processing for Improvement of Biogas Production.

This study investigated acid splitting wastewater (ASW) and interphase (IF) from soapstock splitting, as well as matter organic non glycerol (MONG) from glycerol processing, as potential substrates for biogas production. Batch and semicontinuous thermophilic anaerobic digestion experiments were conducted, and the substrates were preliminary treated using commercial enzymes kindly delivered by Novozymes A/C. The greatest enhancement in the batch digestion efficiency was achieved when three preparations; EversaTransform, NovoShape, and Lecitase were applied in the hydrolysis stage, which resulted in the maximum methane yields of 937 NL/kg VS and 915 NL/kg VS obtained from IF and MONG, respectively. The co-digestion of 68% ASW, 16% IF, and 16% MONG (wet weight basis) performed at an organic loading rate (OLR) of 1.5 kg VS/m3/day provided an average methane yield of 515 NLCH4/kg VSadded and a volatile solid reduction of nearly 95%. A relatively high concentration of sulfates in the feed did not significantly affect the digestion performance but resulted in an increased hydrogen sulfide concentration in the biogas with the peak of 4000 ppm.

Effect of mixing ratio and total solids content on temperature-phased anaerobic codigestion of rice straw and pig manure: Biohythane production and microbial structure

Long-term semi-continuous experiments were carried out under three feedstock conditions to study the effects of mixing ratio and total solids (TS) content on temperature-phased anaerobic codigestion of rice straw (RS) and pig manure (PM). The results showed that biohythane only produced from the mixture with 6% TS content and its average content were 12.83 ± 1.19% (hydrogen) and 23.68 ± 1.12% (methane). Increasing mixture TS content and decreasing its RS ratio increased biohythane production and organic matter removal by creating a suitable process pH and increasing the anaerobic reaction rates. The highest biohythane production of the mixture reached 73.09 ± 3.03 ml/g VS (hydrogen) and 235.81 ± 9.30 ml/g VS (methane) at a mixing ratio of 5:1 and TS content of 6%. A variety of hydrogen-producing bacteria were found in the thermophilic reactor and Clostridium_sensu_stricto_1 played an important role. Butyric acid fermentation is the main hydrogen-producing pathway. Methanobacterium and Methanosaeta were dominant archaea in the mesophilic reactor.

Bioaugmentation with zeolite-immobilized bacterial consortium OPK results in a bacterial community shift and enhances the bioremediation of crude oil-polluted marine sandy soil microcosms

A pyrene-degrading consortium OPK containing Mycolicibacterium strains PO1 and PO2, Novosphingobium pentaromativorans PY1 and Bacillus subtilis FW1 effectively biodegraded medium- and long-chain alkanes as well as mixed hydrocarbons in crude oil. The detection of alkB and CYP153 genes in the genome of OPK members supports its phenotypic ability to effectively degrade a broad range of saturated hydrocarbons in crude oil. Zeolite-immobilized OPK was developed as a ready-to-use bioproduct and it exhibited 74% removal of 1000 mg L−1 crude oil within 96 h in sterilized seawater without nutrient supplementation and maintained high crude oil-removal activity under a broad range of pH values (5.0–9.0), temperatures (30–40 °C) and salinities (20–60‰). In addition, the immobilized OPK retained a high crude oil removal efficacy in semicontinuous experiments and showed reusability for at least 5 cycles. Remarkably, bioaugmentation with zeolite-immobilized OPK in sandy soil microcosms significantly increased crude oil (10,000 mg kg−1 soil) removal from 45% to 80.67% within 21 days compared to biostimulation and natural attenuation. Moreover, bioaugmentation with exogenous immobilized OPK stimulated an increase in the relative abundances of Alcanivorax genus, indigenous hydrocarbon-degrading bacteria, which in turn enhanced removal efficiency of crude oil contamination from sandy soil microcosms. The results indicate positive interactions between the bioaugmented immobilized consortium, harboring Mycolicibacterium as a key player, and indigenous Alcanivorax, which exhibited crucial functions for improving crude oil removal efficacy. The knowledge obtained forms an important basis for further synthesis and handling of a promising bio-based product for enhancing the in situ bioremediation of crude oil-polluted marine environments.

Effects of rice straw ratio on mesophilic and thermophilic anaerobic co-digestion of swine manure and rice straw mixture

The mesophilic and thermophilic anaerobic co-digestion (Co-AD) of swine manure (SM) and rice straw (RS) mixtures was evaluated in lab-scale continuously stirred tank reactors through long-term semi-continuous experiments to investigate the effects of three RS ratios (25%, 33.3%, and 50%, based on total solids). The experimental results showed that an increase in the RS ratio reduced the biogas and methane production, and methane content in both Co-ADs and the effects of the increased RS ratio on the mesophilic Co-AD (Co-MAD) were slightly lower than those on the thermophilic Co-AD (Co-TAD). The digestate characteristics were also affected by the RS ratio. A reduction analysis demonstrated the higher importance of the RS ratio in the substrate with respect to gas production in Co-MAD compared to Co-TAD. The increase in the RS ratio increased the relative abundance of Clostridium_sensu_strricto_1, and changed the predominant archaea and methanogenesis pathways in both Co-ADs.

Residual municipal solid waste as co-substrate at wastewater treatment plants: An assessment of methane yield, dewatering potential and microbial diversity

Separately collected organic fraction of municipal solid waste, also known as biowaste, is typically used to fill the available capacity of digesters at wastewater treatment plants. However, this approach might impair the use of the ensuing digestate for fertilizer production due to the presence of sewage sludge, a contaminated substrate. Worldwide, unsorted municipal solid household waste, i.e. residual waste, is still typically disposed of in landfills or incinerated, despite its high content of biodegradables and recyclables. Once efficiently separated from residual waste by mechanical processes, the biodegradables might be appropriate to substitute biowaste at wastewater treatment plants. Thus, the biowaste would be available for fertilizer production and contribute to a reduction in the demand on non-renewable fertilizers. This study aimed at determining the technical feasibility of co-digesting the mechanically separated organic fraction of residual waste with sewage sludge. Further, key parameters for the implementation of co-digestion at wastewater treatment plants were determined, namely, degradation of the solids and organics, specific methane production, flocculant demand, and dewatered sludge production. The microbial community and diversity in both mono- and co-digestion was also investigated. Semi-continuous laboratory scale experiments showed that the co-substrate derived from the residual waste provided a stable anaerobic co-digestion process, producing 206 to 245 L of methane per kg of volatiles solids added to the digester. The dewaterability of the digestate increased by 4.8 percentage points when the co-substrate was added; however, there was also an increase in the flocculant demand. The specific dewatered sludge production was 955 kg per ton of total solids of co-substrate added to the digester. Amplicon sequencing analysis provided a detailed insight into the microbial communities, which were primarily affected by the addition of co-substrate. The microbiota was fully functional and no inhibition or problems in the anaerobic digestion process were observed after co-substrate addition.