Anaerobic Batch Reactor Research Articles

Mesophilic Process and Kinetics Studies of Selected Biomolecules as Potential Enhancers of Biomethanization of Cow Dung in an Anaerobic Tubular Batch Reactor

Mesophilic biogas production and substrate decomposition is one of the significant limiting steps in biogas generation. The rate of generation and quality often affect the viability of biogas systems. This study assessed the potential for biogas process catalysis using powdered Sorghum bicolor L., Zea mays, and Pennisetum glaucum. The kinetics and biogas generation processes were studied. Experiments were conducted in 1 m3 tubular batch reactors, where batches were dosed with various organic biomolecules. Results show that the use of P. glaucum L. and S. bicolor L. reduced the biogas retention times significantly. Biogas generation commenced after the first day for digesters fed with S. bicolor L. and P. glaucum L. while one with Z. mays and control occurred on day two. The rate of biomethanation and methane content were enhanced. S. bicolor L. led to the highest methane content. Findings reveal that locally available organic biomolecules improved biogas quality and quantity.

Production of Biogas from Kitchen Wastes Generated from the Mess of NIT Agartala

A review has been done on the formulation of mathematical models for designing anaerobic batch reactor for the producing of biogas from solid wastes. Using material balance analysis, the design parameters, especially biokinetic behavior of solid wastes are studied. Hydrolysis constants and reaction orders at both low total solids concentrations and high total solids concentrations were thoroughly reviewed by initial rate method. Population growth model and first order hydrolysis model are also studied. It has been found that if sufficient reaction time is given, in terms of reaction kinetics, the hydrolysis process in kitchen waste fermentation can be described as a first order reaction. An attempt is done by utilizing the biodegradable kitchen waste collected from Aryabhatta hostel, NIT Agartala for generation of biogas and demonstrating the possibilities of energy recovery. A simple anaerobic digester has been fabricated to capture the generated biogas. To produce methane as a clean fuel the use of cow dung as substrate is studied to ferment the kitchen wastes.

Anaerobic digestion of urea pretreated water hyacinth removed from Lake Abaya; bio-methane potential, system stability, and substance conversion.

Water hyacinth (Eichhornia crassipes) is characterized as an aquatic plant that can grow very rapidly and freely float over water, and covers the top surface of water. It prevents the penetration of sunlight and reduces nutrients and oxygen from water bodies, and can adversely affect the aquatic ecosystem; however, it can be used in the biogas production as the sole feedstock for anaerobic digestion due to high contents of carbohydrates and biodegradable matter. Thus, this study was aimed to remove water hyacinth from Lake Abaya as a renewable energy resource for biogas production through anaerobic digestion. A lab-scale anaerobic batch reactor was applied to assess its biogas and methane generation potential. The results showed that the total solids of 91.9% at dry basis and volatile solids of 84.82% of TS. The biogas and methane production potential of 474.92 mL g−1 VS and 213.92 mL g−1 VS was recorded during 45 days HRT at 37 ± 1 °C. The daily methane production discloses accelerated increment starting from day 8 up to the peak point on day 12 (2170 mL d−1). The biochemical conversion of substances in water hyacinth to biogas was recorded as follows: total volatile solids (96.1%), cellulose (92.5%), hemicellulose (88.2%), and chemical oxygen demand (99.3%). Based on results, E. crassipes can be the sole feedstock for the anaerobic reactor to produce biomethane, while the effluents can be applied as organic fertilizers.

Impact of partially submersed iron scraps in simultaneously sulfate and nitrate removal using sulfate-reducing bacteria

In this study, partially submerged iron scraps were allowed to react to the contaminants at the headspace air and liquid interface for pollutants removal in the serum bottle reactors. The experiments were conducted using Box–Behnken design of Response Surface Methodology in anaerobic batch reactors (120 ml) at different concentrations of sulfate (0.5, 1.75, 3 g/L), nitrate (0.25, 0.375, 0.5 g/L) and iron scraps (0, 0.125, 0.250 g/50 ml). The sulfate reducer enriched mixed culture was used for simultaneous removal of SO42− and NO3−. The highest sulfate removal of 49.37 % was achieved at 0 g/50 ml ISs, 3 g/L SO4−2, and 0.375 g/L NO3−. Even at a higher concentration of both SO42− (3 g/L) and NO3−(0.5 g/L), a significant SO42− removal of 44.65% was achieved at an iron concentration of 125mg/50ml accompanied with NO3− conversion. Both the lower and higher concentrations of iron scraps were showing effective interaction at higher SO42− and NO3− levels. The results of the confirmatory experiments with iron scraps of 0.039 g/50 ml with the desirability of 0.92 showed a maximum SO42− removal of 50.62 % with complete conversion of nitrate.

Biomass residues adjacent forest roads in two different forest species (Fagus sylvativa and Pinus brutia): quantities and evaluation of their biogas production potential

In this study the quantity of biomass residues accumulated at a low-altitude Mediterranean forest (pinus and fagus clusters) were evaluated under field conditions. Samples of fresh and dry leaves (litter) were digested in batch anaerobic reactors to evaluate their biogas production potential. The quantity of pine needles and fagus leaves accumulated onto the forest carpet was on average 670 and 1440 g/m2, respectively and they were characterized by a low moisture content (10-11%). The biogas production potential was 100 and 150 L/kg volatile solids for pinus and fagus litter respectively (compared to 140 and 300 L/kg VS for the fresh pine needles and fagus leaves). The data from both field and laboratory studies were used to calculate the biogas yield per km of forest road, if the collected biomass is disposed of to an anaerobic digestion facility. The conceptual model applied revealed that it is possible to recover up to 500 and 1000 m3 CH4 / km, from the pinus and fagus clusters respectively. Concluding, pine needles and fagus leaves are important resources and can be efficiently used for energy production in anaerobic digestion facilities.

Diversified metabolism makes novel Thauera strain highly competitive in low carbon wastewater treatment

Thauera, as one of the core members of wastewater biological treatment systems, plays an important role in the process of nitrogen and phosphorus removal from low-carbon source sewage. However, there is a lack of systematic understanding of Thauera’s metabolic pathway and genomics. Here we report on the newly isolated Thauera sp. RT1901, which is capable of denitrification using variety carbon sources including aromatic compounds. By comparing the denitrification processes under the conditions of insufficient, adequate and surplus carbon sources, it was found that strain RT1901 could simultaneously use soluble microbial products (SMP) and extracellular polymeric substances (EPS) as electron donors for denitrification. Strain RT1901 was also found to be a denitrifying phosphate accumulating bacterium, able to use nitrate, nitrite, or oxygen as electron acceptors during poly-β-hydroxybutyrate (PHB) catabolism. The annotated genome was used to reconstruct the complete nitrogen and phosphorus metabolism pathways of RT1901. In the process of denitrifying phosphorus accumulation, glycolysis was the only pathway for glycogen metabolism, and the glyoxylic acid cycle replaced the tricarboxylic acid cycle (TCA) to supplement the reduced energy. In addition, the abundance of conventional phosphorus accumulating bacteria decreased significantly and the removal rates of total nitrogen (TN) and chemical oxygen demand (COD) increased after the addition of RT1901 in the low carbon/nitrogen (C/N) ratio of anaerobic aerobic anoxic-sequencing batch reactor (AOA-SBR). This research indicated that the diverse metabolic capabilities of Thauera made it more competitive than other bacteria in the wastewater treatment system.

Deciphering the transfers of antibiotic resistance genes under antibiotic exposure conditions: Driven by functional modules and bacterial community

Antibiotics can exert selective pressures on sludge as well as affect the emergence and spread of antibiotic resistance genes (ARGs). However, the underlying mechanisms of ARGs transfers are still controversial and not fully understood in sludge system. In present study, two anaerobic sequence batch reactors (ASBR) were constructed to investigate the development of ARGs exposed to two sulfonamide antibiotics (SMs, sulfadiazine SDZ and sulfamethoxazole SMX) with increasing concentrations. The abundance of corresponding ARGs and total ARGs obviously increased with presence of SMs. Functional analyses indicated that oxidative stress response, signal transduction and type IV secretion systems were triggered by SMs, which would promote ARGs transfers. Network analysis revealed 18 genera were possible hosts of ARGs, and their abundances increased with SMs. Partial least-squares path modeling suggested functional modules directly influenced mobile genetic elements (MGEs) as well as the ARGs might be driven by both functional modules and bacteria community, while bacteria community composition played a more key role. Sludge with refractory antibiotics (SDZ) may stimulate the relevant functions and shift the microbial composition to a greater extent, causing more ARGs to emerge and spread. The mechanisms of ARGs transfers are revealed from the perspective of functional modules and bacterial community in sludge system for the first time, and it could provide beneficial directions, such as oxidative stress reduction, cellular communication control, bacterial composition directional regulation, for ARGs spread controlling in the future.

Management and kinetics of methane production from anaerobic batch reactors treating PET bottle washing wastewater

The study evaluated the methanogenic potential of anaerobic sludge in Wastewater from the Washing of PET (Polyethylene terephthalate) bottles sent for Recycling (WWPR). The bioreactors were inoculated with sludge from an upflow anaerobic sludge blanket reactor treating poultry waste. The operation occurred under anaerobic conditions at 35 °C and 150 rpm for three bioreactors in triplicate with the initial COD concentration of 2000 mg L−1 (C1), 5000 mg L−1 (C2), and 10,000 mg L−1 (C3). The inhibition in the anaerobic biological treatment caused by high surfactant concentration impaired the wastewater biodegradation. COD removals were 67.8 ± 0.4% (C1), 67.6 ± 2.7% (C2), and 59.1 ± 2.9% (C3), indicating a process inhibition in the latter condition. The modified Gompertz model indicated a cumulative methane production of 290 mL for condition C1 with an adjustment coefficient of 99.11%. The methane potential for the production of electricity revealed a maximum annual production of 188,292 MWh. Annual thermal energy from condition C1 could produce 1.01 × 108 PET bottles. Therefore, the anaerobic treatment of WWPR is an alternative to wastewater management, avoiding greenhouse gases emission and potentiating the generation of electrical and thermal energy.

Improving biological treatment of textile wastewater

Abstract Textile industries are among the primary contributors of water pollution. Treatment of textile wastewater is very important before discharging it to the environment. In the present study, laboratory-scale anaerobic batch reactors were used for co-treatment of a mixture of textile and domestic wastewater at 37 °C. The objective of this work was to investigate optimum conditions for the anaerobic co-digestion of textile wastewater and domestic wastewater. Domestic wastewater as a carbon source to enhance treatment of textile wastewater in color and other pollutants removal was examined. Textile and domestic wastewater were mixed at different proportions to make a total volume of 500 mL. Proportions of domestic wastewater and retention time were two main factors studied in influencing pollutant removal efficiency. Optimum conditions for removal of pollutants were 18 days' residence time at 60 and 40% textile and domestic wastewater respectively. The removal efficiencies were 52.8, 58.3 and 51.6% for Color, BOD and COD, respectively. Phosphorus (PO43−), Ammonium (NH3-N) and Nitrate (NO3-) increased at 78.5, 49 and 87% respectively. However, the concentration levels were above Tanzania Bureau of Standards (TBS) discharge limits. Post treatment is suggested to achieve standard discharge limits.

Gradual development of ammonia-induced syntrophic acetate-oxidizing activities under mesophilic and thermophilic conditions quantitatively tracked using multiple isotopic approaches

Insights into microbiota adaptation to increased ammonia stress, and identification of indicator microorganisms can help to optimize the operation of anaerobic digesters. To identify microbial indicators and investigate their metabolic contribution to acetoclastic methanogenesis (AM), syntrophic acetate oxidation (SAO) or hydrogenotrophic methanogenesis (HM), 40 anaerobic batch reactors fed with acetate of 110 mmol/L were set up at NH4+-N concentrations of 0.14 g/L, 5.00 g/L or 7.00 g/L, inoculated with thermophilic or mesophilic microbiota with or without pre-exposure to ammonia stress. Four stable carbon isotope probing approaches were applied in parallel, with [1,2-13C]-CH3COOH, [2-13C]-CH3COOH, [13C]NaHCO3 or non-labeled CH3COOH used individually. The last three approaches were used to quantify the methanogenic pathways by tracking labeled 13C or natural 13C signatures in the resulting CH4 and CO2, and consistently detected the dynamic transition of dominant pathways from AM to SAO-HM under ammonia stress. Results of quantitative PCR and fluorescence in-situ hybridization illustrated the procedure, acetotrophic methanogens being outcompeted by acetate-oxidizing syntrophs. The first and last isotope-labeling approaches were designed to probe the active acetate-mineralizing microbes with DNA-SIP. Known acetate-oxidizing bacteria like Syntrophaceticus and Tepidanaerobacter, as well as novel members of Pseudomonas, Bacillus and Symbiobacteraceae were detected, with Methanoculleus as the predominant H2/CO2-utilizing partner. Using NanoSIMS, some bacterial cells were observed to be fixing CO2 from [13C]NaHCO3. In this study, Methanosaeta was only active with ammonia < 200 mg-N/L; the syntrophs catalyzing SAO-HM started to compete with AM-conducting Methanosarcina at intermediate concentrations of ammonia, i.e. 200–500 mg-N/L, and outcompeted the acetotrophic methanogens with ammonia > 500 mg-N/L. Under ammonia stress, diverse known and novel microbial taxa were involved in acetate mineralization, comparable with those identified in previous studies.

The effect of reduced graphene oxide addition on methane production from municipal organic solid waste

AbstractBACKGROUNDConductive materials have become the focus of recent studies to accelerate and stabilize the conversion of organic wastes to methane in anaerobic digestion processes. In this study, the effect of the addition of reduced graphene oxide (rGO) on biogas/biomethane production from municipal organic solid wastes in anaerobic batch reactors was investigated. In this context, the effect of loading ratios (0, 0.5, 1 and 2 gVS inoculum (gVS nutrient)−1) and rGO addition at different concentrations (0, 10, 20 and 30 mg L−1) was examined during a 45‐day study period.RESULTSThe highest biogas production reached a level of 816 ± 14 mL (gVS)−1 when substrate/inoculum ratio was 1 and 20 mg L−1 rGO was added (50% more than the group without rGO added). Addition of 30 mg L−1 rGO resulted in 667 ± 12 mL (gVS)−1 corresponding to 23% higher biogas production compared to the control reactor without rGO. The highest cumulative biomethane production was observed to be 525 ± 20 mL (gVS)−1 in the reactor with 20 mg L−1 rGO added in which substrate/inoculum ratio was 1. In the reactors with 10 and 30 mg L−1 and without rGO addition biomethane productions were 448 ± 21, 401 ± 13 and 323 ± 23 mL (gVS)−1, respectively.CONCLUSIONSResults revealed that the addition of rGO increased biomethane production from municipal organic solid wastes. It is concluded that rGO addition has the potential to be applied for real‐scale facilities within the scope of renewable energy production and circular economy. © 2021 Society of Chemical Industry

Insight into microbial community diversity and composition of two-stage anaerobic digestion: Focusing methanogenic stage

This work characterized microbial community composition and diversity of the ‘methanogenic phase’ of a two-staged anaerobic sequence batch reactor(ASBR). The ASBR was operated for biogas production from abattoir wastewater, heterogeneous fruits-vegetables solid waste, and their combinations. The Metagenomic DNA of digestate from the ASBRs was extracted and amplified with sample-specific primers targeting the (V3-V4) hypervariable regions of the 16S rRNA gene. The 16S rRNA Amplicons were sequenced using the Illumina MiSeq. The overall microbial composition was influenced by the nature of substrates. The sequence analysis revealed that the methanogenic stage ASBRs were dominated by bacterial and archaeal members most closely related to Proteobacteria, Firmicutes, Planctomycetes, and Euryarchaeota. Out of identified methanogens genera, Methanosaeta and Methanosarcina were the most dominant. Compared to Methanosarcina, the unclassified spp. of a member of the Methanosaeta genus was the most dominant. This implied the Methanosaeta spp. were mainly responsible for the biomethanation of the substrates.

Enhanced biogas production from anaerobic digestion of wastewater from the fruit juice industry by sonolysis: experiments and modelling.

The aim of this study is to investigate the use of ultrasound pretreatment as potential technique to solubilize organic matter and fermentation of fruit juice effluents in anaerobic batch reactor. The efficacy of ultrasound pretreatment has been assessed at low frequency of 20 kHz and at different sonication times (20, 40 and 60 min). Compared with control, the amount of biogas produced increased by 47, 57 and 60% for sonication times of 20, 40 and 60 min, respectively. Methane content of the produced biogas was about 59% in the control and 64% in the case of effluent subjected to ultrasonication for 60 min. After 20 days of anaerobic digestion of the fruit juice effluents, the efficiency of chemical oxygen demand (COD) increased by 9, 31 and 35% with respect to control for sonication times of 20, 40 and 60 min, respectively, corresponding to total sugars uptake efficiency of about 35, 51 and 54%, respectively. The modified Gompertz equation was used to describe the cumulative biogas production. A good agreement was found between simulated and experimental data.

Anaerobic membrane bioreactor for the production of bioH2: Electron flow, fouling modeling and kinetic study

This study investigated the evaluation of a new operational protocol for increasing the membrane lifetime during bioH2 production by the anaerobic membrane bioreactor-sequencing batch reactor (AnMBR-SBR) along with a kinetic and membrane fouling study. The certified electron (e-) flow model was applied to investigate the structure of microbial community and metabolism pathway. The AnMBR-SBR was operated under varying applied organic loading rates (OLR). At applied OLR of 0.5 g COD/L.d, the bioH2 production was around 0.39 ± 0.21 L/d, and an increase of applied OLR to 8.0 g COD/L.d led to improve bioH2 production to 14.57 ± 9.06 L/d. At the OLR of 0.5 g COD/L.d, the dominant e- sinks were acetate (52.2%) and butyrate (22.5%). While significant augmentation in butyrate production (49.9%) was observed at OLR of 8.0 g COD/L.d, indicating that bioH2 production was followed by acetate/butyrate pathway. According to the e- flow model, NADH2 balance error at OLR of 0.5 and 1.0 g COD/L.d ranged 3–8%, demonstrating the ferredoxin:hydrogenase system as the main route of bioH2 production by the spore-forming H2 producing bacteria viz., Clostridium or Ethanoligenes species. For other OLRs, the error balance of NADH2 ranged from 21 to 24%, indicating the activation of non-spore-forming bacteria, e.g., Enterobacter, Escherichia, or Klebsiella species that coincide with the spore-forming bacteria.

Artificial intelligence modeling to predict transmembrane pressure in anaerobic membrane bioreactor-sequencing batch reactor during biohydrogen production

The complex nature of wastewater treatment has led to search for alternative strategies such as different artificial intelligence (AI) techniques to model the various operational parameters. The present work is aimed at predicting the transmembrane pressure (TMP) as a key operational parameter in the case of anaerobic membrane bioreactor-sequencing batch reactor (AnMBR-SBR) during biohydrogen production using the adaptive neuro-fuzzy inference systems (ANFIS) and artificial neural network (ANN). In both the models, organic loading rates (OLR) ranging from 0.5 to 8.0 g COD/L/d, effluent pH (3.6–6.9), mixed liquor suspended solid (4.6–21.5 g/L) and mixed liquor volatile suspended solid (3.7–15.5 g/L) were used as the input parameters to test TMP as an output parameter. The ANFIS model was trained using the hybrid algorithms for TMP prediction. The higher prediction performance was obtained by using the Gauss membership function with four membership numbers. A back-propagation algorithm was also employed for the feed forward training of ANN model; the best structure was a Levenberg-Marquardt training algorithm with nine neurons in the hidden layer. By employing ANFIS and ANN models, relatively a good prediction of TMP was obtained with the R2 values of 0.93 and 0.88, respectively while the calculated mean square error for TMP in the ANFIS model (7.3 × 10−3) was lower than that of ANN model (8.02 × 10−3). The higher R2 and lower MSE values for the ANFIS model exhibited a better TMP prediction performance than the ANN model. Finally, it was observed that in the sensitivity analysis of ANN model, OLR was the most important input parameter on the variation of TMP.

Formaldehyde biodegradation in an ASBR-SBR system: an effective treatment solution for furniture industry painting booth wastewater

Formaldehyde (HCHO) is a toxic organic compound with carcinogenic properties which is present in the furniture industry painting booth wastewater (PBW) and does not receive adequate treatment in its industrial environment. This effluent treatment commonly occurs by physicochemical processes that do not remove formaldehyde, while advanced treatment methods are costly for industrial scale application. This study assessed a system consisting of an anaerobic sequential batch reactor (ASBR) followed by an aerobic sequential batch reactor (SBR) for the PBW treatment. The system performance was evaluated by the gradual increase of HCHO concentration from 34 ± 5 to 232 ± 10 mg HCHO L−1, and chemical oxygen demand (COD) from 585 ± 8.4 to 3960 ± 100 mg O2 L−1, performed with cycle time of 4 days in ASBR and 2 days in SBR, evaluating the formaldehyde potential toxicity on anaerobic biomass. The ASBR-SBR system removed 99% of COD and HCHO until initial concentration of 180 ± 7 mg HCHO L−1. The HCHO concentration increase to 232 ± 10 mg L−1 reduced the removal efficiency of organic matter to 72% in ASBR due to partial inhibition of microorganisms caused by formaldehyde toxicity. However, under these conditions, the SBR was efficient and removed the remaining organic matter by 98%. The performance of ASBR-SBR showed that this simple system was suitable for the PBW treatment at the evaluated concentrations.

A Study on the Reaction Kinetics of Anaerobic Microbes Using Batch Anaerobic Sludge Technique for Beverage Industrial Wastewater

In this study, a low-cost, efficient, and environmentally friendly anaerobic sludge process for the treatment of industrial beverage wastewater was investigated to analyze the effect of bacteria growth on the degradation of organic matter (chemical oxygen demand). Additionally, the mechanism, interactions between the microbe’s growth, and operating conditions of an anaerobic batch reactor along with the wastewater treatment efficiency were evaluated via microbial kinetics. The kinetic coefficients based on chemical oxygen demand (COD) by conventional techniques such as kinetic coefficients growth yield (0.46 mg VSS/mg COD), saturation coefficient (3500 mg/L COD), the maximum rate of substrate utilization per unit mass of biomass (0.0066 mg/L COD), growth rate by Monod equation, M (0.03833 L/h), and maximum growth rate, μm (0.03672 L/h) were calculated. The results show a higher rate of substrate degradation (0.54 day−1) due to the high COD removal efficiency (CRE) of 99.31% during 13 days that was achieved, which can be attributed to the active involvement of anaerobic microbes in the process of degradation. Based on these results, it can be concluded that the current study can be used as an effective way to analyze the industrial beverage wastewater at commercial levels.

Role of waste-based geopolymer spheres addition for pH control and efficiency enhancement of anaerobic digestion process.

In anaerobic digestion processes, pH has a vital role due to the direct impacts on the microbial community. An eco-friendly approach has been applied to control pH in anaerobic bioreactors, using waste-containing fly ash geopolymer spheres (GS) instead of powdered chemical compounds, to promote continuous alkalis leaching. The influence of GS porosity and concentration on the behavior of anaerobic sequential batch reactor treating cheese whey was evaluated. Results showed that the use of GS with the highest concentration and porosity promoted an increase in methane yield up to 30%, compared to the assay with powdered chemical compounds addition. In addition, GS boosted butyric acid production to the detriment of propionic acid, which favored methane production by a factor up to 1.2. This innovative approach indicates that GS addition can regulate pH in anaerobic digesters treating challenging wastewaters and, simultaneously, improve not only its efficiency but also the sustainability of the entire process.

A Performance Comparison of Anaerobic and an Integrated Anaerobic-Aerobic Biological Reactor System for the Effective Treatment of Textile Wastewater

The accumulation of recalcitrant azo dyes from untreated textile effluents has adversely impacted the ecosystem. The immense stability in their nature is conferred by the presence of azo bonds (N=N) in their structure. The reduction of this azo bond occurs exclusively under anaerobic conditions giving rise to colorless aromatic amines, which are carcinogenic. In the present study, a synthetic textile effluent containing mixed azo dyes such as Reactive Red, Reactive Black, and Reactive Brown, was treated using activated sludge under anaerobic conditions in a lab-scale anaerobic sequential batch reactor (An-SBR). At a concentration of 100 mg/L of mixed azo dyes, the An-SBR gave a maximum of 88% decolorization detected through UV-visible spectroscopy. Physicochemical analyses revealed 73% removal of BOD, 90% TDS removal, 69% COD removal, 4.05% TKN removal, 66% chloride removal, and 73% hardness removal. When the concentration of dyes was increased to 500 mg/L, the treatment showed a decrease in decolorization efficiency. This was then compared to a sequential anaerobic-aerobic treatment process performed in An-SBR and a laboratory-scale aerobic moving bed biofilm reactor (MBBR). The study revealed that the sequential process held more potential for commercial application than exclusively an anaerobic process. The metabolites formed during the treatment phase were extracted and analyzed by FT-IR and HPLC and identified through GC-MS analyses and were compared to those found in the untreated effluent. A phytotoxicity test was conducted on the remainder (secondary) sludge using Vigna unguiculata, and it was found to show a 50% reduction in germination and retardation in root and shoot length.

Biofilters are potential hotspots for H2S production in brackish and marine water RAS

The production of hydrogen sulphide (H2S) is a major concern and challenge in marine land-based recirculating aquaculture systems (RAS). In order to gain a thorough understanding on H2S production dynamics in RAS, an anaerobic batch reactors experiment was performed, evaluating the production potential of total dissolved sulphide (TDS) and H2S and characterizing the microbial communities in different RAS environments (solid waste, biomedia+RAS-water, biomedia+seawater [SW], and RAS-water) during 33 days. The highest H2S concentrations were achieved in the reactors with biomedia+RAS-water, where biofilms growing on biomedia hosted a high abundance of sulphate reducing bacteria (SRB), which activated once anoxic conditions and carbon sources were introduced. The biofilms in the biomedia+SW reactors produced lower amounts of H2S than the biomedia+RAS-water reactors, due to the lower abundance of SRB. The solid waste produced H2S at low rate, the production being limited by the substrate competition between SRB and other microbial groups. No production of H2S was observed in the reactors with only RAS-water, due to the absence of SRB and suitable carbon sources. Based on measurements of production of H2S in this study, a moving bed biofilter submerged in brackish water (17 ppt) can potentially produce 139 g of H2S per biofilter m3, when the biomedia is not adequately mixed and oxygenated. Altogether, the results demonstrate that although SRB are found both in biofilters and solid waste, these two environments exhibit different H2S production dynamics. Biofilters produce large quantities of H2S under anoxic conditions, while solid waste deposited to the rearing tanks exhibits a lower but constant production of H2S. However, both of these H2S sources can be suppressed through fast removal of solids from rearing tanks and optimal operational conditions for biofilters.