The potential of osmolytes and their precursors to alleviate osmotic stress of anaerobic granular sludge

Effects of salinity on glycerol conversion and biological phosphorus removal by aerobic granular sludge

Industrial wastewater often has high levels of salt, either due to seawater or e.g. sodium chloride (NaCl) usage in the processing. Previous work indicated that aerobic granular sludge (AGS) is differently affected by seawater or saline water at similar osmotic strength. Here we investigate in more detail the impact of NaCl concentrations and seawater on the granulation and conversion processes for AGS wastewater treatment. Glycerol was used as the carbon source since it is regularly present in industrial wastewaters, and to allow the evaluation of microbial interactions that better reflect real conditions. Long-term experiments were performed to evaluate and compare the effect of salinity on granulation, anaerobic conversions, phosphate removal, and the microbial community. Smooth and stable granules as well as enhanced biological phosphorus removal (EBPR) were achieved up to 20 g/L NaCl or when using seawater. However, at NaCl levels comparable to seawater strength (30 g/L) incomplete anaerobic glycerol uptake and aerobic phosphate uptake were observed, the effluent turbidity increased, and filamentous granules began to appear. The latter is likely due to the direct aerobic growth on the leftover substrate after the anaerobic feeding period. In all reactor conditions, except the reactor with 30 g/L NaCl, Ca. Accumulibacter was the dominant microorganism. In the reactor with 30 g/L NaCl, the relative abundance of Ca. Accumulibacter decreased to ≤1 % and an increase in the genus Zoogloea was observed. Throughout all reactor conditions, Tessaracoccus and Micropruina, both actinobacteria, were present which were likely responsible for the anaerobic conversion of glycerol into volatile fatty acids. None of the glycerol metabolizing proteins were detected in Ca. Accumulibacter which supports previous findings that glycerol can not be directly utilized by Ca. Accumulibacter. The proteome profile of the dominant taxa was analysed and the results are further discussed. The exposure of salt-adapted biomass to hypo-osmotic conditions led to significant trehalose and PO43--P release which can be related to the osmoregulation of the cells. Overall, this study provides insights into the effect of salt on the operation and stability of the EBPR and AGS processes. The findings suggest that maintaining a balanced cation ratio is likely to be more important for the operational stability of EBPR and AGS systems than absolute salt concentrations.

Impact of Polyethylene-Glycol-Induced Water Potential on Methane Yield and Microbial Consortium Dynamics in the Anaerobic Degradation of Glucose

This study investigated the relationship between water potential (Ψ) and the cation-induced inhibition of methane production in anaerobic digesters. The Ψ around methanogens was manipulated using polyethylene glycol (PEG) in a batch anaerobic reactor, ranging from -0.92 to -5.10 MPa. The ultimate methane potential (Bu) decreased significantly from 0.293 to 0.002 Nm3 kg-1-VSadded as Ψ decreased. When Ψ lowered from -0.92 MPa to -1.48 MPa, the community distribution of acetoclastic Methanosarcina decreased from 59.62% to 40.44%, while those of hydrogenotrophic Methanoculleus and Methanobacterium increased from 17.70% and 1.30% to 36.30% and 18.07%, respectively. These results mirrored changes observed in methanogenic communities affected by cation inhibition with KCl. Our findings strongly indicate that the inhibitory effect of cations on methane production may stem more from the water stress induced by cations than from their direct toxic effects. This study highlights the importance of considering Ψ dynamics in understanding cation-mediated inhibition in anaerobic digesters, providing insights into optimizing microbial processes for enhanced methane production from organic substrates.

Enhancing microbial salt tolerance through low-voltage stimulation for improved p-chloronitrobenzene (p-CNB) removal in high-salinity wastewater

As an important raw material for the synthesis of chemical and pharmaceutical, hazardous carcinogen p-chloronitrobenzene (p-CNB) has been widely found in high-salinity wastewater which need to be treated carefully. Due to the high-salinity shock on microorganisms, conventional microbial treatment technologies usually show poor effluent quality. This study initially investigated the p-CNB removal performance of microorganisms stimulated by 1.2 V low-voltage in high-salinity wastewater under facultative anaerobic conditions and further revealed the enhanced mechanisms. The results showed that the p-CNB removal kinetic parameter kp-CNB in the electrostimulating microorganism reactor (EMR) increased by 104.37 % to 155.30 % compared to the microorganism reactor (MR) as the control group under the varying salinities (0-45 g/L NaCl). The secretion of extracellular polymeric substances (EPS) in halotolerant microorganisms mainly enhanced by 1.2 V voltage stimulation ranging from 0 g/L NaCl to 30 g/L NaCl. Protein concentration ratio of EMR to MR in loosely bound EPS achieved maximum value of 1.77 at the salinity of 15 g/L NaCl, and the same ratio in tightly bound EPS also peaked at 1.39 under the salinity of 30 g/L NaCl. At the salinity of 45 g/L NaCl, 1.2 V voltage stimulation mainly enhanced salt-in strategy of halotolerant microorganisms, and the intracellular Na+ and K+ concentration ratio of EMR to MR reached maximum and minimum values of 0.65 and 1.92, respectively. Furthermore, the results of microbial metagenomic and metatranscriptomic analysis showed the halotolerant microorganisms Pseudomonas_A and Nitratireductor with p-CNB removal ability were enriched significantly under 1.2 V voltage stimulation. And the gene expression of p-CNB removal, salt-in strategy and betaine transporter were enhanced under voltage stimulation at varying salinities. Our investigation provided a new solution which combined with 1.2 V voltage stimulation and halotolerant microorganisms for the treatment of high-salinity wastewater.

Insight into the effect of rice-straw ash on enhancing the anaerobic digestion performance of high salinity organic wastewater

Anaerobic digestion is an economic method for treating high salinity organic wastewater (HSOW), but performance enhancement is needed because of the inhibitory effect of high salinity. In this study, rice-straw ash (RSA) was applied to alleviate the inhibitory effect during HSOW anaerobic digestion. The results showed that, when the NaCl content increased from 0% to 3.0%, the methane production decreased by 87.35%, and the TOC removal rate decreased to 34.12%. As a K+ and alkalinity source, RSA addition enhanced the anaerobic digestion performance, and the optimal dosage was 0.88 g/L. Under this dosage, the methane production increased by 221.60%, and TOC removal rate reached 66.42% at 3.0% salinity. The addition of RSA increased the proportion of living cells in the high salinity environment, and enhanced the activity of key enzymes and electron transfer efficiency in the anaerobic digestion process. The addition of RSA with a dosage of 0.88 g/L promoted the accumulation of acetoclastic methanogen Methanothrix. The abundance of substrate transporters, ion transporters and electron transfer related functional genes were enriched, which might be key for promoting HSOW anaerobic digestion performance. The results also showed that RSA addition played an important role in maintaining the stability of the anaerobic digestion system, and it could be a potential strategy for enhancing the anaerobic digestion performance under high salinity conditions.

Conductive materials enhance microbial salt-tolerance in anaerobic digestion of food waste: Microbial response and metagenomics analysis

Previous studies have shown that high salinity environments can inhibit anaerobic digestion (AD) of food waste (FW). Finding ways to alleviate salt inhibition is important for the disposal of the growing amount of FW. We selected three common conductive materials (powdered activated carbon, magnetite, and graphite) to understand their performance and individual mechanisms that relieve salinity inhibition. Digester performances and related enzyme parameters were compared. Our data revealed that under normal and low salinity stress conditions, the anaerobic digester ran steady without significant inhibitions. Further, the presence of conductive materials promoted conversion rate of methanogenesis. This promotion effect was highest from magnetite > powdered activated carbon (PAC) > graphite. At 1.5% salinity, PAC and magnetite are beneficial in maintaining high methane production efficiency while control and the graphite added digester acidified and failed rapidly. Additionally, metagenomics and binning were used to analyze the metabolic capacity of the microorganisms. Some species enriched by PAC and magnetite possessed higher cation transport capacities and were to accumulate compatible solutes. PAC and magnetite promoted direct interspecies electron transference (DIET) and syntrophic oxidation of butyrate and propionate. Also, the microorganisms had more energy available to cope with salt inhibition in the PAC and magnetite added digesters. Our data imply that the promotion of Na+/H+ antiporter, K+ uptake, and osmoprotectant synthesis or transport by conductive materials may be crucial for their proliferation in highly stressful environments. These findings will help to understand the mechanisms of alleviate salt inhibition by conductive materials and help to recover methane from high-salinity FW.

Deciphering the fate of osmotic stress priming on enhanced microorganism acclimation for purified terephthalic acid wastewater treatment with high salinity and organic load

Osmotic stress priming (OSP) was an effective management strategy for improving microbial acclimation to salt stress. In this study, the interaction between pollutants and microbiota, and microbial osmoregulation were investigated triggered by OSP (alternately increasing salinity and organic loading). Results showed that OSP significantly improved COD removal from 31.53 % to 67.99 % and mitigated the terephthalate inhibition produced by toluate, decreasing from 1908.08 mg/L to 837.16 mg/L compared with direct priming. Due to an increase in salinity, Pelotomaculum and Mesotoga were enriched to facilitate terephthalate degradation and syntrophic acetate oxidation (SAO). And organic load promoted acetate formation through syntrophic metabolism of Syntrophorhabdus/Pelotomaculum and SAO-dependent hydrogenotrophic methanogenesis. K⁺ absorbing, proline and trehalose synthesis participated in osmoregulation at 0.5 % salinity, while only ectoine alleviated intracellular osmolarity under 1.0 % salinity with OLR of 0.44 kg COD /m³. This study provided in-depth insight for microbial acclimation process of anaerobic priming of saline wastewater.

Enhanced anaerobic reduction of nitrobenzene at high salinity by betaine acting as osmoprotectant and regulator of metabolism

Anaerobic technology is extensively applied in the treatment of industrial organic wastewater, but high salinity always triggers microbial cell dehydration, causing the failure of the anaerobic process. In this work, betaine, one kind of compatible solutes which could balance the osmotic pressure of anaerobic biomass, was exogenously added for enhancing the anaerobic reduction of nitrobenzene (NB) at high salinity. Only 100 mg L^-1 betaine dosing could significantly promote the removal efficiency of NB within 35 h at 9% salinity (36.92 ± 4.02% without betaine and 72.94 ± 6.57% with betaine). The relieving effects on salt stress could be observed in the promotion of more extracellular polymeric substances (EPS) secretion with betaine addition. Additionally, the oxidation-reduction potential (ORP), as well as the electron transfer system (ETS) value, was increased with betaine addition, which was reflected in the improvement of system removal efficiency and enzyme activity. Microbial community analysis demonstrated that Bacillus and Clostridiisalibacter which were positively correlated with the stability of the anaerobic process were enriched with betaine addition at high salinity. Metagenomic analysis speculated that the encoding genes for salt tolerance (kdpB/oadA/betA/opuD/epsP/epsH) and NB degradation (nfsA/wrbA/ccdA/menC) obtained higher relative abundance with betaine addition under high salt environment, which might be the key to improving salt tolerance of anaerobic biomass. The long-term assessment demonstrated that exogenous addition betaine played an important role in maintaining the stability of the anaerobic system, which would be a potential strategy to achieve a high-efficiency anaerobic process under high salinity conditions.

Glutamate Enhances Osmoadaptation of Anammox Bacteria under High Salinity: Genomic Analysis and Experimental Evidence

An osmoprotectant that alleviates the bacterial osmotic stress can improve the bioreactor treatment of saline wastewater. However, proposed candidates are expensive, and osmoprotectants of anammox bacteria and their ecophysiological roles are not fully understood. In this study, a comparative analysis of 34 high-quality public metagenome-assembled genomes from anammox bacteria revealed two distinct groups of osmoadaptation. Candidatus Scalindua and Kuenenia share a close phylogenomic relation and osmoadaptation gene profile and have pathways for glutamate transport and metabolisms for enhanced osmoadaptation. The batch assay results demonstrated that the reduced Ca. Kuenenia activity in saline conditions was substantially alleviated with the addition and subsequent synergistic effects of potassium and glutamate. The operational test of two reactors demonstrated that the reduced anammox performance under brine conditions rapidly recovered by 35.7-43.1% as a result of glutamate treatment. The Ca. Kuenenia 16S rRNA and hydrazine gene expressions were upregulated significantly (p < 0.05), and the abundance increased by approximately 19.9%, with a decrease in dominant heterotrophs. These data demonstrated the effectiveness of glutamate in alleviating the osmotic stress of Ca. Kuenenia. This study provides genomic insight into group-specific osmoadaptation of anammox bacteria and can facilitate the precision management of anammox reactors under high salinity.

Functional Insights of Salinity Stress-Related Pathways in Metagenome-Resolved Methanothrix Genomes

Recently, methanogenic archaea belonging to the genus Methanothrix were reported to have a fundamental role in maintaining stable ecosystem functioning in anaerobic bioreactors under different configurations/conditions. In this study, we reconstructed three Methanothrix metagenome-assembled genomes (MAGs) from granular sludge collected from saline upflow anaerobic sludge blanket (UASB) reactors, where Methanothrix harundinacea was previously implicated with the formation of compact and stable granules under elevated salinity levels (up to 20 g/L Na⁺). Genome annotation and pathway analysis of the Methanothrix MAGs revealed a genetic repertoire supporting their growth under high salinity. Specifically, the most dominant Methanothrix (MAG_279), classified as a subspecies of Methanothrix_A harundinacea_D, had the potential to augment its salinity resistance through the production of different glycoconjugates via the N-glycosylation process, and via the production of compatible solutes as N^ε-acetyl-β-lysine and ectoine. The stabilization and reinforcement of the cell membrane via the production of isoprenoids was identified as an additional stress-related pathway in this microorganism. The improved understanding of the salinity stress-related mechanisms of M. harundinacea highlights its ecological niche in extreme conditions, opening new perspectives for high-efficiency methanisation of organic waste at high salinities, as well as the possible persistence of this methanogen in highly-saline natural anaerobic environments.

IMPORTANCE Using genome-centric metagenomics, we discovered a new Methanothrix harundinacea subspecies that appears to be a halotolerant acetoclastic methanogen with the flexibility for adaptation in the anaerobic digestion process both at low (5 g/L Na⁺) and high salinity conditions (20 g/L Na⁺). Annotation of the recovered M. harundinacea genome revealed salinity stress-related functions, including the modification of EPS glycoconjugates and the production of compatible solutes. This is the first study reporting these genomic features within a Methanothrix sp., a milestone further supporting previous studies that identified M. harundinacea as a key-driver in anaerobic granulation under high salinity stress.

Application of a Spiral Symmetric Stream Anaerobic Bioreactor for treating saline heparin sodium pharmaceutical wastewater: Reactor operating characteristics, organics degradation pathway and salt tolerance mechanism

In this study, a Spiral Symmetry Stream Anaerobic Bioreactor (SSSAB) was adopted for treating actual saline heparin sodium pharmaceutical wastewater (HSPW). After adaptation, under the influent COD of 8731 mg/L, OLR of 6.98 kg COD/(m³•d) and salinity of 3.57 wt%, the COD removal reached up to 82%. This value is much higher than the reported for the other reactors at similar salinity. Benzenes are the major organic compounds in HSPW. The main rate-limiting steps are the degradations of phenol and p-cresol. In addition, the degradation pathways of typical benzenes in HSPW were analyzed. After adaptation, the soluble salt content in the granular sludge increased, and the bacterial extracellular polymers (EPS), especially tightly-bound EPS also significantly increased. 16S rRNA analysis revealed that the microbial community in the anaerobic granular sludge (AGS) had become adapted to the HSPW treatment since Mesotoga (12.4%), Anaerophaga (9.0%), Oceanotoga (6.1%) and Aminobacterium (4.1%) increased from previously below 1.0% values. The relative abundance of Methanosarcina in the upper layer of the reactor (68.7%) is significantly higher than that at the bottom (3.8%). This proves the superiority of the SSSAB structure. Finally, a model for salt-tolerant microorganisms is given, which proposes a mechanism for this study and provides reference for other anaerobic biological treatments of high-salt containing wastewater.

Abscisic Acid in Coordination with Nitrogen Alleviates Salinity-Inhibited Photosynthetic Potential in Mustard by Improving Proline Accumulation and Antioxidant Activity

This investigation was done to assess the role of abscisic acid (ABA; 25 µM) and/or nitrogen (N; 10 mM) in the alleviation of salinity (NaCl; 100 mM)-induced reduction in photosynthetic activity and growth, N and sulfur (S) assimilation of mustard (Brassica juncea L.) cv. RH0-749. Salinity treatment caused oxidative stress and significantly elevated the content of both H2O2 and thiobarbituric acid reactive substances (TBARS), and impaired photosynthetic activity and growth, but increased the content of nitrogenous osmolyte proline and the activity of antioxidant enzymes involved in the metabolism of reactive oxygen species. The application of 25 µM ABA under a controlled condition negatively affected photosynthesis and growth. However, ABA, when combined with N, minimized oxidative stress and mitigated the salinity-inhibited effects by increasing the activity of antioxidant enzymes (superoxide dismutase, SOD; glutathione reductase, GR; ascorbate peroxidase, APX) and proline content. Overall, the supplementation of 10 mM N combined with 25 µM ABA provides an important strategy for enhancing the photosynthetic potential of B. juncea under saline conditions.

Salinity enhances high optically active L-lactate production from co-fermentation of food waste and waste activated sludge: Unveiling the response of microbial community shift and functional profiling

Lactic acid (LA), a versatile platform molecule, can be fermented from organic wastes, such as food waste and waste activated sludge. In this study, an efficient approach using salt, a component of food waste as an additive, was proposed to increase LA production. The LA productivity was increased at 10 g NaCl/L and optical pure L-lactate was obtained at 30 g NaCl/L. The enhancement of LA was in accordance with the increased solubilization and the critical hydrolase activities under saline conditions. Moreover, high salinity (30-50 g NaCl/L) changed the common conversion of LA to volatile fatty acids. In addition, the key LA bacteria genera (Bacillus, Enterococcus, Lactobacillus) were selectively enriched under saline conditions. Strong correlations between salinity and functional genes for L-LA production were also observed. This study provides a practical way for the enrichment of L-LA with high optical activity from organic wastes.

Trehalose as an osmolyte in Candidatus Accumulibacter phosphatis

Abstract

Candidatus Accumulibacter phosphatis is an important microorganism for enhanced biological phosphorus removal (EBPR). In a previous study, we found a remarkable flexibility regarding salinity, since this same microorganism could thrive in both freshwater- and seawater-based environments, but the mechanism for the tolerance to saline conditions remained unknown. Here, we identified and described the role of trehalose as an osmolyte in Ca. Accumulibacter phosphatis. A freshwater-adapted culture was exposed to a single batch cycle of hyperosmotic and hypo-osmotic shock, which led to the release of trehalose up to 5.34 mg trehalose/g volatile suspended solids (VSS). Long-term adaptation to 30% seawater-based medium in a sequencing batch reactor (SBR) gave a stable operation with complete anaerobic uptake of acetate and propionate along with phosphate release of 0.73 Pmol/Cmol, and complete aerobic uptake of phosphate. Microbial analysis showed Ca. Accumulibacter phosphatis clade I as the dominant organism in both the freshwater- and seawater-adapted cultures (> 90% presence). Exposure of the seawater-adapted culture to a single batch cycle of hyperosmotic incubation and hypo-osmotic shock led to an increase in trehalose release upon hypo-osmotic shock when higher salinity is used for the hyperosmotic incubation. Maximum trehalose release upon hypo-osmotic shock was achieved after hyperosmotic incubation with 3× salinity increase relative to the salinity in the SBR adaptation reactor, resulting in the release of 11.9 mg trehalose/g VSS. Genome analysis shows the possibility of Ca. Accumulibacter phosphatis to convert glycogen into trehalose by the presence of treX, treY, and treZ genes. Addition of trehalose to the reactor led to its consumption, both during anaerobic and aerobic phases. These results indicate the flexibility of the metabolism of Ca. Accumulibacter phosphatis towards variations in salinity.

Key points

• Trehalose is identified as an osmolyte in Candidatus Accumulibacter phosphatis.

• Ca. Accumulibacter phosphatis can convert glycogen into trehalose.

• Ca. Accumulibacter phosphatis clade I is present and active in both seawater and freshwater.

Electronic supplementary material

The online version of this article (10.1007/s00253-020-10947-8) contains supplementary material, which is available to authorized users.

Cation exchange membrane behaviour of extracellular polymeric substances (EPS) in salt adapted granular sludge

This paper aims to elucidate the role of extracellular polymeric substances (EPS) in regulating anion and cation concentrations and toxicity towards microorganisms in anaerobic granular sludges adapted to low (0.22 M of Na⁺) and high salinity (0.87 M of Na⁺). The ion exchange properties of EPS were studied with a novel approach, where EPS were entangled with an inert binder (PVDF-HFP) to form a membrane and characterized in an electrodialysis cell. With a mixture of NaCl and KCl salts the EPS membrane was shown to act as a cation exchange membrane (CEM) with a current efficiency of ∼80%, meaning that EPS do not behave as ideal CEM. Surprisingly, the membrane had selectivity for transport of K⁺ compared to Na⁺ with a separation factor ( [Formula: see text] ) of 1.3. These properties were compared to a layer prepared from a model compound of EPS (alginate) and a commercial CEM. The alginate layer had a similar current efficiency (∼80%.), but even higher [Formula: see text] of 1.9, while the commercial CEM did not show selectivity towards K⁺ or Na⁺, but exhibited the highest current efficiency of 92%. The selectivity of EPS and alginate towards K⁺ transport has interesting potential applications for ion separation from water streams and should be further investigated. The anion repelling and cation binding properties of EPS in hydrated and dehydrated granules were further confirmed with microscopy (SEM-EDX, epifluorescence) and ion chromatography (ICP-OES, IC) techniques. Results of specific methanogenic activity (SMA) tests conducted with 0.22 and 0.87 M Na⁺ adapted granular sludges and with various monovalent salts suggested that ions which are preferentially transported by EPS are also more toxic towards methanogenic cells.

Biological phosphorus removal in seawater-adapted aerobic granular sludge

Seawater can be introduced or intrude in sewer systems and can thereby negatively influence biological wastewater treatment processes. Here we studied the impact of artificial seawater on the enhanced biological phosphate removal (EBPR) process performance by aerobic granular sludge (AGS) with synthetic wastewater. Process performance, granule stability and characteristics as well as microbial community of a seawater-adapted AGS system were observed. In seawater conditions strong and stable granules formed with an SVI₅ of 20 mL/g and a lower abrasion coefficient than freshwater-adapted granules. Complete anaerobic uptake of acetate, anaerobic phosphate release of 59.5 ± 4.0 mg/L PO₄^3--P (0.35 mg P/mg HAc), and an aerobic P-uptake rate of 3.1 ± 0.2 mg P/g VSS/h were achieved. The dominant phosphate accumulating organisms (PAO) were the same as for freshwater-based aerobic granular sludge systems with a very high enrichment of Ca. Accumulibacter phosphatis clade I, and complete absence of glycogen accumulating organisms. The effect of osmotic downshocks was tested by replacing influent seawater-based medium by demineralized water-based medium. A temporary decrease of the salinity in the reactor led to a decreased phosphate removal activity, while it also induced a rapid release of COD by the sludge, up to 45.5 ± 1.7 mg COD/g VSS. This is most likely attributed to the release of osmolytes by the cells. Recovery of activity was immediately after restoring the seawater feeding. This work shows that functioning of aerobic granular sludge in seawater conditions is as stable as in freshwater conditions, while past research has shown a negative effect on operation of AGS processes with NaCl-based wastewater at the same salinity as seawater.

Enhancement of COD removal in constructed wetlands treating saline wastewater: Intertidal wetland sediment as a novel inoculation

This study investigated intertidal wetland sediment (IWS) as a novel inoculation source for saline wastewater treatment in constructed wetlands (CWs). Samples of IWS (5-20 cm subsurface sediment), which are highly productive and rich in halophilic and anaerobic bacteria, were collected from a high-salinity natural wetland and added to CW matrix. IWS-supplemented CW microcosms that are planted and unplanted Phragmites australis were investigated under salty (150 mM NaCl: PA+(S) and CT+(S)) and non-salty (0 mM NaCl: PA+ and CT+) conditions. The chemical oxygen demand (COD) removal potential of IWS-supplemented CWs was compared with that of conventional CWs without IWS (PA(S) and CT(S), PA, and CT). Results showed that the COD removal rate was higher in PA+(S) (51.80% ± 3.03%) and CT+(S) (29.20% ± 1.26%) than in PA(S) (27.40% ± 3.09%) and CT(S) (27.20% ± 3.06%) at 150 mM NaCl. The plants' chlorophyll content and antioxidant enzyme activity indicated that the addition of IWS enhanced the resistance of plants to salt. Microbial community analysis showed that the dominant microorganisms in PA+(S) and CT+(S), namely, Anaerolineae, Desulfobacterales, and Desulfuromonadales, enhanced the organic removal rates via anaerobic degradation. IWS-induced Dehalococcoides, which is a key participant in ethylene formation, improved the plants' stress tolerance. Several halophilic/tolerant microorganisms were also detected in the CW system with IWS. Thus, IWS is a promising inoculation source for CWs that treat saline wastewater.

Nitrogen alleviates salinity toxicity in Solanum lycopersicum seedlings by regulating ROS homeostasis

The present study was aimed to investigate adaptation in physiology and biochemistry of Solanum lycopersicum seedlings under NaCl (NaCl₀; 0.0 g NaCl kg^-1 sand, NaCl₁; 0.3 g NaCl/kg sand and NaCl₂; 0.5 g NaCl/kg sand) stress, simultaneously supplemented with different (deprived; 0 mg/kg sand, LN; 105 mg/kg sand, MN; 210 mg/kg sand and HN; 270 mg/kg sand) levels of nitrogen (N). NaCl at both doses caused significant loss in growth, K⁺ content, K⁺/Na⁺ ratio, total chlorophyll and photosynthetic oxygen evolution. Further, N supplementation influences growth of test seedlings, that attained maximum growth in HN followed by MN, LN and deprived N conditions. N at HN level significantly declined Na⁺ accumulation in the cell and enhanced level of K⁺. NaCl treatment enhanced level of oxidative stress biomarkers: superoxide radical (O₂^•-), hydrogen peroxide (H₂O₂), MDA equivalents contents and electrolyte leakage in leaf as well as root despite enhanced activity of SOD, POD, CAT and GST, and enzymes participating in the ascorbate-glutathione cycle (AsA-GSH cycle) viz. APX, DHAR and GR. At the same time, higher contents of total AsA (AsA + DHA) and total GSH (GSH + GSSG), and maintained ratios of AsA/DHA and GSH/GSSG in HN fed seedlings were observed. Overall, the results suggest that HN supplementation was able in alleviating NaCl induced toxicity in test seedlings which was mainly due to the up-regulation of the AsA-GSH cycle, K⁺ and K⁺/Na⁺ ratio, which resulted into better growth performance of HN fed seedlings under NaCl stress while reverse was noticed for LN and deprive N conditions.

Photosynthetic bacteria improved hydrogen yield of combined dark- and photo-fermentation

Integration of dark- and photo-fermentation is a promising strategy to enhance saline wastewater treatment efficiency and biohydrogen production. In this study, dark- and photo-fermentative bacterial consortium was respectively enriched and their communities were analyzed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Both consortia were mainly composed of hydrogen-producing strains. After the first-stage dark-fermentation, the following conditions were applied prior to the second-stage fermentation: fermentative broth pH regulation (the pH group), glucose addition (the glucose group), glucose addition and pH regulation (the glucose + pH group), photosynthetic bacteria addition (the photo group), and photosynthetic bacteria addition and pH regulation (the photo + pH group), respectively. Dark fermentative broth with no pretreatment was used as control (the control group). Then the second stage began. The results showed that pH restriction had more influence than substrate or products restriction on dark-fermentative hydrogen production. Addition of photo-fermentative bacteria after dark-fermentation increased the hydrogen yield (134%) and substrate utilization (67%). These findings indicated syntrophic interactions between dark- and photo-fermentative bacteria during the hydrogen production process.

A Brief Review of Anaerobic Digestion of Algae for Bioenergy

The potential of algal biomass as a source of liquid and gaseous biofuels has been the subject of considerable research over the past few decades, with researchers strongly agreeing that algae have the potential of becoming a viable aquatic energy crop with a higher energy potential compared to that from either terrestrial biomass or municipal solid waste. However, neither microalgae nor seaweed are currently cultivated solely for energy purposes due to the high costs of harvesting, concentrating and drying. Anaerobic digestion of algal biomass could theoretically reduce costs associated with drying wet biomass before processing, but practical yields of biogas from digestion of many algae are substantially below the theoretical maximum. New processing methods are needed to reduce costs and increase the net energy balance. This review examines the biochemical and structural properties of seaweeds and of microalgal biomass that has been produced as part of the treatment of wastewater, and discusses some of the significant hurdles and recent initiatives for producing biogas from their anaerobic digestion.