Anaerobic Digestion Effluent Research Articles

Combining Geobacter spp. Dominated Biofilms and Anaerobic Digestion Effluents─The Effect of Effluent Composition and Electrode Potential on Biofilm Activity and Stability.

The combination of anaerobic digestion (AD) and microbial electrochemical technologies (METs) offers different opportunities to increase the efficiency and sustainability of AD processes. However, methanogenic archaea and/or particles may partially hinder combining MET and AD processes. Furthermore, it is unclear if the applied anode potential affects the activity and efficiency of electroactive microorganisms in AD-MET combinations as it is described for more controlled experimental conditions. In this study, we confirm that 6-week-old Geobacter spp. dominated biofilms are by far more active and stable in AD-effluents than 3-week-old Geobacter spp. dominated biofilms. Furthermore, we show that the biofilms are twice as active at -0.2 V compared to 0.4 V, even under challenging conditions occurring in AD-MET systems. Paired-end amplicon sequencing at the DNA level using 16S-rRNA and mcrA gene shows that hydrogenotrophic methanogens incorporate into biofilms immersed in AD-effluent without any negative effect on biofilm stability and electrochemical activity.

Nitrogen and carbon removal from anaerobic digester effluents with low carbon to nitrogen ratios under feammox conditions

Removal of nitrogen and carbon from anaerobic digester (AD) effluents is challenging for currently available technologies. Herein, effective treatment for real AD effluents was achieved via the feammox process by using a Multistage Feammox Bioreactor (MSFB). The reactor achieved the best performance with AD effluent of a low carbon to nitrogen (C/N) ratio of 2.5. A 6-day retention time reached removal efficiencies for NH4+ and COD at 99 % and 97 %, respectively, with a thorough conversion of NH4+ to N2. Accordingly, the MSFB achieved removal rates for N and C of 14 and 34 mg L−1 d−1, respectively. The C/N ratio of 2.5 is regarded to be the critical point above which the feammox is shifted to conventional iron reduction with organic carbon. Iron-reducing bacteria of the γ- Proteobacteria (Pseudomonas and Acinetobacter), and δ- Proteobacteria (Geobacter) were dominant in the MSFB and were supposed to drive the feammox process.

Evaluation of flue gas desulfurization gypsum as a low-cost precipitant for phosphorus removal from anaerobic digestion effluent filtrate

Land application of anaerobic digestion (AD) effluent as a fertilizer is desirable for nutrient recycle, but often supplies excess phosphorus (P), which contributes to surface water eutrophication. Reducing the P content in AD effluent using calcium treatment prior to land application is a potential strategy for improving effluent disposability. In order to solve the problems of low phosphorus removal efficiency and high operating cost in wastewaters, this study took flue gas desulphurization (FGD) gypsum, a by-product of coal-fired power plants, as a low-cost calcium source, and combined with traditional phosphorus removal agents to achieve high phosphorus removal efficiency with less chemical inputs. As the results showed, FGD gypsum dosages of 20 mM Ca (3.44 g/L) and 40 mM Ca (6.89 g/L) removed up to 97.1% of soluble P (initially 102.8 mg/L) within 60-90 minutes. Combining FGD gypsum treatment with traditional chemical treatments using Ca(OH)2 or FeCl3 could achieve >99% P removal with reduced chemical costs. This study demonstrated that FGD gypsum is an effective calcium precipitant for phosphorus removal.

Biological conversion of methane to methanol at high H2S concentrations with an H2S-tolerant methanotrophic consortium

To develop biological biogas to methanol conversion technology without costly hydrogen sulfide (H2S) removal, a high H2S tolerant methanotrophic consortium (HTMC), was enriched from an anaerobic digester effluent in presence of 5.64 g/m3 H2S in the gas phase. The HTMC can grow stably and produce methanol under conditions with CH4/air mixtures containing 5.64 g/m3 of H2S. There is no significant (p > 0.05) difference in cell yield or CH4 to methanol conversion efficiency between trials with different H2S concentrations from 0 g/m3 to 5.64 g/m3. Under optimal conditions, a cell yield of 0.333 g cells/g CH4, a methanol concentration of 0.28 mg/mL, and a CH4 to methanol conversion efficiency of 0.22 mol/mol were obtained, respectively. Besides methanotrophs (14.85%) and other bacteria, Cyanobacteria were also identified in the HTMC with a high abundancy (32.16%), which could broaden the application of HTMC for simultaneous utilization of CH4 and CO2 from raw biogas.

DEGRADATION OF ORGANIC POLLUTANTS IN FLOCCULATED LIQUID DIGESTATE USING PHOTOCATALYTIC TITANATE NANOFIBERS: MECHANISM AND RESPONSE SURFACE OPTIMIZATION

<List> <ListItem> <ItemContent> ● Titanate NFs were synthesized and photodegraded liquid digestate for the first time. </ItemContent> </ListItem> <ListItem> <ItemContent> ● The long titanate NFs (bandgap of 3.16 eV) have a high VFA removal rate of 72.9%. </ItemContent> </ListItem> <ListItem> <ItemContent> ● RSM has been used to optimize the VFA, COD, and color removal rate. </ItemContent> </ListItem> <ListItem> <ItemContent> ● The quadratic model and the effects of photocatalytic dosage were significant. </ItemContent> </ListItem> </List> Titanate nanofibers (TNFs) were synthesized using a hydrothermal method and were employed for the first time in this study to photocatalytically degrade organic pollutants found in flocculated liquid digestate of poultry litter. The photocatalytic performance of TNFs, with a bandgap of 3.16 eV, was tested based on degradation of organic pollutants and removal of color. Five combinations of pollutant concentration and pH were examined (0.2 to 1.3 g·L⁻¹ at pH 4 to 10). Central composite design (CCD) and response surface methodology (RSM) were applied in order to optimize the removal rates of volatile fatty acids (VFA) and chemical oxygen demand (COD), and the decolorization rate. There were no significant differences between the regression models generated by the CCD/RSM and the experimental data. It was found that the optimal values for pH, dosage, VFA removal rate, COD removal rate and decolorization rate were 6.752, 0.767 g·L⁻¹, 72.9%, 59.1% and 66.8%, respectively. These findings indicates that photocatalytic TNFs have potential for the posttreatment of anaerobic digestion effluent, as well as other types of wastewater.

Growth Parameters of Various Green Microalgae Species in Effluent from Biogas Reactors: The Importance of Effluent Concentration.

The use of liquid waste as a feedstock for cultivation of microalgae can reduce water and nutrient costs and can also be used to treat wastewater with simultaneous production of biomass and valuable products. This study applied strategies to treat diluted anaerobic digester effluent (ADE) as a residue of biogas reactors with moderate (87 ± 0.6 mg L-1; 10% ADE) and elevated NH4+-N levels (175 ± 1.1 mg L-1; 20% ADE). The effect of ADE dilution on the acclimatization of various microalgae was studied based on the analysis of the growth and productivity of the tested green algae. Two species of the genus Chlorella showed robust growth in the 10-20% ADE (with a maximum total weight of 3.26 ± 0.18 g L-1 for C. vulgaris and 2.81 ± 0.10 g L-1 for C. sorokiniana). The use of 10% ADE made it possible to cultivate the strains of the family Scenedesmaceae more effectively than the use of 20% ADE. The growth of Neochloris sp. in ADE was the lowest compared to other microalgal strains. The results of this study demonstrated the feasibility of introducing individual green microalgae into the processes of nutrient recovery from ADE to obtain biomass with a high protein content.

Benchmarking sidestream shortcut nitrogen removal processes against nitrous oxide recovery from a life cycle perspective

Anaerobic digestion effluent adds significantly to nutrient loading, energy consumption, and emissions of wastewater treatment plants. Sustainably treating this ammonia-rich sidestream requires systematic analysis on environmental impacts of shortcut nitrogen removal processes. Coupled Aerobic–Anoxic Nitrous Decomposition Operation (CANDO) is a novel biotechnology for sidestream nitrogen removal with energy recovery potential from N2O. Nevertheless, the environmental impacts of CANDO remain unknown after initial scale-up studies. In this study, three sidestream treatment processes, namely, nitritation-denitritation, nitritation-anammox, and CANDO, integrated with mainstream anaerobic-anoxic-oxic (A2O) treatment routes, are assessed by process simulation and life cycle assessment (LCA). The results show that the nitritation-anammox process has the smallest effect on human health, ecosystem quality, and resource availability among the three routes. Furthermore, the global warming potential generated from the CANDO-A2O process is 157 kg CO2 eq per cubic meter of anaerobic digestion liquid treated, which is slightly higher than nitritation-anammox-A2O (132 kg CO2 eq) but remarkably lower than nitritation-denitritation-A2O (248 kg CO2 eq). With low carbon emission and promising alternatives for carbon source, the CANDO-A2O route exhibits great potential in achieving carbon neutrality. This work is the first to quantitatively evaluate the potential environmental impacts of CANDO from a life cycle perspective, providing insights on the adoption and optimization of shortcut nitrogen removal processes in sidestream treatment.

Mathematical Modeling of Microalgal Growth during Anaerobic Digestion Effluent Bioremediation

The development of kinetic models aims at predicting the behavior of a system or analyzing the underlying mechanisms. This process is essential for understanding microalgal growth and optimizing culture conditions. In the case of microalgal cultivation in wastewater, the analysis becomes even more difficult as growth is often inhibited by several factors, such as nutrient limitation and light inadequacy. In this context, a mathematical model was developed to describe the microbial growth of the species Parachlorella kessleri in different reactor setups using either sterile or non-sterile anaerobic digestion effluent as a substrate. Three different mass balances were taken into consideration to describe biomass growth, phosphorus, and nitrogen consumption. Concerning biomass growth, the logistic model was applied to evaluate the inhibition in biomass formation due to lack of illumination. The maximum optical density under which these species could grow was quantified with an ODmax parameter, which was estimated at 4.07 AU/cm for the Erlenmeyer flask and 2.79 AU/cm for cylindrical photobioreactors. Regarding the nitrogen mass balance, two different terms concerning microalgal assimilation and ammonia stripping were implemented into the equation. The proposed model predicted biomass growth with high accuracy in model training (R2 = 0.90) and validation (R2 = 0.89).

Improvement of biogas production and quality by addition of struvite precipitates derived from liquid anaerobic digestion effluents of palm oil wastes

When biogas is produced, the liquid anaerobic digestion effluents (LADE) still contain pollutants. Struvite precipitation is a technique for reducing pollutants as well as recovering useful elements such as nitrogen, phosphorus, and magnesium. This study aims to precipitate struvite from LADE and use it as an additive to palm oil mill effluent (POME) feedstocks in subsequent biogas production systems (batch and continuous operational modes). Struvite precipitation was simply performed using NaOH at a pH range of 8–10 without external sources of magnesium and phosphorus. The result showed that the optimum pH for struvite precipitation was 9, giving the highest yield and purity of struvite. The addition of 5% struvite to POME feedstock improved the performance of biogas production in the continuous stirred tank reactor (CSTR) in terms of stability, high COD removal efficiencies, increased methane yields, and decreased H2S concentrations. The greatest methane yield of 509.8 mL/g-VS and the methane concentration of 65.10% were obtained in the CSTR. The significant decrease in H2S concentration in biogas can increase the energy content of biogas, save on the cost of H2S removal, reduce corrosion, and extend the operating time of gas turbines used for electricity production. The results of this study emphasize the role of integrating struvite precipitation with continuous biogas production in improving the process sustainability and economy. Struvite precipitation from LADE diminishes the polluted wastewater, decreases the long-term process problems of fouling and clogging caused by struvite, and improves the performance of the biogas production.

Sustainable ammonia recovery from anaerobic digestion effluent through pretreating the feed by biomass ash

Ammonia recovery from anaerobic digestion (AD) effluent by vacuum membrane distillation (VMD) is a sustainable and low-carbon footprint strategy for nitrogen fertilizer production and waste treatment. However, due to the good buffering performance of AD effluent, lots of alkali chemicals are consumed to adjust the pH value, thereby increasing the treatment cost. To reduce the consumption of alkali chemicals, biomass ash (BA) is proposed as the alternative to replace the alkali chemical for pretreating the AD effluent before ammonia recovery in this study. Compared with the case using NaOH for pH adjustment, the ammonia separation factor increases by 40 % for BA addition case. Meanwhile, the 30-h VMD experiment for AD effluent treatment is conducted to testify to the stability. Additionally, the high germination index (GI) value (0.84) illustrates the potential of ammonia-removed AD effluent in agricultural applications. Furthermore, the greenhouse emission of ammonia recovery from AD effluent pretreated with BA is only 2.06 kg-CO2 eq/kg, which decreases by 51 % compared with that of the Haber-Bosch process. Finally, BA addition adopted for AD effluent pretreatment has economic superiority to NaOH addition. Inferably, using BA to pretreat the AD effluent can be acted as a high-efficacy and sustainable candidate strategy for ammonia recovery.

Enhancing the Ammonia Selectivity by Using Nanofiber PVDF Composite Membranes Fabricated with Functionalized Carbon Nanotubes.

Conventional hydrophobic membrane-based membrane distillation (MD) has been applied for ammonia recovery from an anaerobic digestion (AD) effluent. However, the typical hydrophobic membranes do not have selectivity for ammonia and water vapor, which results in high energy consumption from the water evaporation. To enhance the selectivity during the ammonia recovery process, the functionalized carbon nanotubes (CNTs)/polyvinylidene fluoride (PVDF) nanofiber membranes were fabricated by electrospinning, and the effects of different CNTs and their contents on the performance of nanofiber membranes were investigated. The results indicate that CNTs can be successfully incorporated into nanofibers by electrospinning. The contact angles of the composite membrane are all higher than those of commercial membrane, and the highest value 138° can be obtained. Most importantly, under the condition of no pH adjustment, the ammonia nitrogen transfer coefficient reaches the maximum value of 3.41 × 10-6 m/s, which is about twice higher than that of commercial membranes. The ammonia separation factor of the carboxylated CNT (C-CNT) composite membrane is higher than that of the hydroxylated CNT(H-CNT) composite membrane. Compared with the application of the novel C-CNT composite membrane, the ammonia separation factor is 47% and 25% higher than that of commercial and neat PVDF membranes. This work gives a novel approach for enhancing ammonia and water selectivity during AD effluent treatment.

Post-treatment Efficiency Evaluation of Anaerobic Digestion Effluent through Bio-electrochemical Biochemical Methane Potential Test

Post-treatment Efficiency Evaluation of Anaerobic Digestion Effluent through Bio-electrochemical Biochemical Methane Potential Test

Ammonia recovery from anaerobic digestion effluent by aeration-assisted membrane contactor

The ammonia recovery from anaerobic digestion (AD) effluent offers a low cost and low carbon footprint strategy for N recovery. To enhance ammonia recovery performance, the aeration-assisted membrane contactor (MC) process was presented with aeration applied on the feed side. The ammonia recovery performance with different pH adjustment methods and operating parameters were tested. Results illustrated that a high ammonia mass transfer coefficient (Kov = 4.85 ×10−7 m/s) could be achieved in the aeration-assisted MC. With the increase in air flow rate from 0 L/min to 0.6 L/min, the Kov increased from 1.21 × 10−7 m/s to 4.85 × 10−7 m/s by about 300%, and the ammonia separation factor (St) increased from 5.75 to 8.91 by about 55%. Additionally, the Kov increased sharply with the increase in feed temperature. Notably, the ammonia removal efficiency can reach 82% after 6-h experiment, which might be due to the large contact area of membrane contactor and the high mass transfer efficiency caused by the optimal conditions. The greenhouse gas (GHG) emission evaluation showed that compared with that of Haber-Bosch process (4.2 kg-CO2 eq/kg-N), the GHG emission of aeration-assisted MC was 1.86 kg-CO2 eq/kg-N under room temperature. The aeration-assisted MC can provide a high-efficient and low GHG-emission ammonia recovery process.

Fate of antibiotic resistance genes and class 1 integrons during sludge treatment using pilot-scale anaerobic digestion with thermal hydrolysis pretreatment

This work evaluated the fate of antibiotic resistance genes (ARGs) and class 1 integron gene in sewage sludge before and after pilot-scale thermal hydrolysis pretreatment (THP) and subsequent mesophilic anaerobic digestion (AD) treatment. Variables investigated include THP temperatures, feedstock types, and AD solids retention times. Real-time polymerase chain reaction was performed to quantify the ARGs in feedstocks, THP and AD effluent. Results show that THP significantly (t test, p < 0.05) reduced the absolute abundances of most ARGs, with the reduction ranging from 0.03 to 3.09 log units. Rebound effects of ARGs in the subsequent AD were observed and were relevant with tested variables; shorter solids retention time (10 days) and higher THP temperature (165 ℃) can significantly reduce ARGs in AD effluent. These findings provide references about the effects of the THP and AD on the control of ARG spread from sewage sludge to environments.

Economic optimization of hollow fiber membrane contactors for ammonia nitrogen recovery from anaerobic digestion effluents

This study presents the optimization and economic analysis of the membrane contactors to recover ammonia nitrogen from anaerobic effluents. The effects of ammonia nitrogen concentrations and alkalinity of the anaerobic effluents on the operating cost and total recovery cost were investigated, and the optimization of wastewater flowrate and pH was carried out.The sensitivity analysis revealed that the wastewater pH was the dominant parameter of the operating cost, followed by the percentage Am-n recovery and wastewater flowrate. The increase of anaerobic effluent’s alkalinity reduced the optimized wastewater pH and flow rate. The total operating recovery cost, including the production cost of solid ammonium sulfate, was found to be in the range of 0.16–0.31 USD/ kg·ammonium sulfate for the Am-n and alkalinity concentrations of 100–700 mg/L and 400–2800 mg/L as CaCO3, respectively, which are much lower than those of the conventional vacuum thermal stripping/acid absorption technique. The total costs, considering the capital investment of the membrane contactor’s unit, were also determined, and found to be 0.242–0.741 USD/kg·ammonium sulfate in the investigated range of anaerobic effluents

Ecotoxicological response of Spirulina platensis to coexisted copper and zinc in anaerobic digestion effluent.

Copper ion (Cu2+) and zinc ion (Zn2+) are widely co-existent in anaerobic digestion effluent as typical contaminants. This work aims to explore how Cu2+-Zn2+ association affects physiological properties of S. platensis using Schlösser medium (SM) and sterilized anaerobic digestion effluent (SADE). Microalgae cells viability, biochemical properties, uptake of Cu2+ and Zn2+, and risk assessment associated with the biomass reuse as additives to pigs were comprehensively assessed. Biomass production ranged from 0.03 to 0.28 g/L in SM and 0.63 to 0.79 g/L in SADE due to the presence of Cu2+ and Zn2+. Peak value of chlorophyll-a and carotenoid content during the experiment decreased by 70-100% and 40-100% in SM, and by 70-77% and 30-55% in SADE. Crude protein level reduced by 4-41% in SM and by 65-75% in SADE. The reduction ratio of these compounds was positively related to the Cu2+ and Zn2+ concentrations. Maximum value of saturated and unsaturated fatty acids was both obtained at 0.3 Cu + 2.0 Zn (50.8% and 22.8%, respectively) and 25% SADE reactors (33.8% and 27.7%, respectively). Uptake of Cu in biomass was facilitated by Zn2+ concentration (> 4.0 mg/L). Risk of S. platensis biomass associated with Cu2+ was higher than Zn2+. S. platensis from SM (Cu2+ ≤ 0.3 mg/L and Zn2+ ≤ 4.0 mg/L) and diluted SADE (25% and 50% SADE) reactors could be used as feed additives without any risk (hazard index <1), which provides sufficient protein and fatty acids for pig consumption. These results revealed the promising application of using S. platensis for bioremediation of Cu2+ and Zn2+ in anaerobic digestion effluent and harvesting biomass for animal feed additives.

Combined electrochemical treatment coupled to anaerobic digestion effluents

Electrochemical treatment is an effective method to improve physicochemical characteristics of effluents and to minimize the environmental footprint of anaerobic digestion facilities. In the present research an anaerobic digester effluent was subjected to post-treatment, using electro-oxidation or electrocoagulation processes for significant reduction of Chemical oxygen demand and ammonia. A combined electro-oxidation and electrocoagulation treatment was also performed. Results show satisfactory decrease of both Chemical oxygen demand and ammonium nitrogen, which however were relative to the method applied, the time duration and the current intensity. A combined use of both methods may be the best solution for the post-treatment of this high burden effluent. All the presented values have occurred from experiments in the Chemistry Department of the International Hellenic University.

A continuous protein-rich Chlorella sp. HL-1 production system in piggery anaerobic digestion effluent

A continuous protein-rich Chlorella sp. HL-1 production system in piggery anaerobic digestion effluent

PH-depended flushing in an automatized batch leach bed reactor system for volatile fatty acid production

In a two-stage CSTR system, the anaerobic digestion effluent from the second stage (methane reactor) can be used for pH-control in the acidification reactor. But using batch leach bed reactors, controlling the pH-value is key affecting factor due to dynamic process conditions. The aim of this work was to study, an automatized technical-scale leach bed reactor system for VFA-production with pH-dependent flushing. It was developed and tested at mesophilic and thermophilic operating conditions and compared to a time-controlled flushing mode. The reactors were fed with grass silage and the experiments were run for 35 days. Total cumulative VFA yields up to 270 g kg-1VS were achieved and extracted from the reactor. The methane formation in the leach bed reactors was successfully suppressed with a pH-controlled flushing mode. As a result of the extraction of the VFA from the leach bed reactors, the methane potential decreased by up to 50 %.

The sustainable utilization of anaerobic digestion effluents treating in suspended filler algae assisted systems

Significant amounts of anaerobic digestion effluents (ADE) containing high concentration of inorganic salts (source of nitrogen and phosphorus) and hardly degradable organic matter are produced during the generation of biogas using livestock manure. Without appropriate treatment, the imbalanced carbon to nitrogen ratio may lead to severe pollution of the environment. Considering different environmentally friendly processes such as recycling, energy regeneration, and sustainable development, suspended fillers were added to traditional algal-bacterial symbiosis (ABS) systems. In the present research, three systems including suspended filler algae assisted bio-reactor (SFA-PBR), no filler algae assisted bio-reactor (NFA-PBR), and single activated sludge system (ABS) were examined. Changes in bacterial communities were analyzed using high throughput sequencing. In addition, the mechanisms of ADE degradation in the presence and absence of suspended algae fillers were studied by comparing their effect on the degradation of COD (chemical oxygen demand), TN (total nitrogen), AN (ammonia nitrogen), and TP (total phosphorus). Systems where the ratio of active microalgae to bacteria was higher promoted the interaction between the two types of microorganisms, accelerating the stability of the ABS. Thus, the daily COD degradation rate in the stage was still high. Flora such as microalgae and bacteria were embedded in the filler spheres, which increased the microorganisms resistance to the poor environment induced by high concentrations of inorganic nutrients and organic matter present in the ADE. This favored the sustainable water utilization of ADE. After the treatment in the SFA-PBR system, the COD degradation rate was 75.32 %. The effluent COD concentration was 334.21 ± 39.18 mg/L. TN and AN degradation rates were 89.34 and 91.32%, respectively. The TN and AN concentrations in the effluent were 35.42 ± 2.65 and 29.97 ± 2.65 mg/L, respectively. The degradation rate of TP was 95.39 %. The effluent TP concentration was 0.86 ± 0.18 mg/L. The Chao diversity and ACE index values in the SFA-PBR system were higher than those of other groups. This result further supports the conclusion formulated with the Shannon diversity index result. Specifically, the effective sequence in the SFA-PBR system group presented a higher degree of homogeneity and abundance.