A review of anaerobic treatment of saline wastewater

Biofilm formation and granule properties in anaerobic digestion at high salinity

For the anaerobic biological treatment of saline wastewater, Anaerobic Digestion (AD) is currently a possibility, even though elevated salt concentrations can be a major obstacle. Anaerobic consortia and especially methanogenic archaea are very sensitive to fluctuations in salinity. When working with Upflow Sludge Blanket Reactor (UASB) technology, in which the microorganisms are aggregated and retained in the system as a granular biofilm, high sodium concentration negatively affects aggregation and consequently process performances. In this research, we analysed the structure of the biofilm and granules formed during the anaerobic treatment of high salinity (at 10 and 20 g/L of sodium) synthetic wastewater at lab scale. The acclimated inoculum was able to accomplish high rates of organics removal at all the salinity levels tested. 16S rRNA gene clonal analysis and Fluorescence In Situ Hybridization (FISH) analyses identified the acetoclastic Methanosaeta harundinacea as the key player involved acetate degradation and microbial attachment/granulation. When additional calcium (1 g/L) was added to overcome the negative effect of sodium on microbial aggregation, during the biofilm formation process microbial attachment and acetate degradation decreased. The same result was observed on granules formation: while calcium had a positive effect on granules strength when added to UASB reactors, Methanosaeta filaments were not present and the degradation of the partially acidified substrate was negatively influenced. This research demonstrated the possibility to get granulation at high salinity, bringing to the forefront the importance of a selection towards Methanosaeta cells growing in filamentous form to obtain strong and healthy granules.

Enrichment of extremophilic exoelectrogens in microbial electrolysis cells using Red Sea brine pools as inocula

Applying microbial electrochemical technologies for the treatment of highly saline or thermophilic solutions is challenging due to the lack of proper inocula to enrich for efficient exoelectrogens. Brine pools from three different locations (Valdivia, Atlantis II and Kebrit) in the Red Sea were investigated as potential inocula sources for enriching exoelectrogens in microbial electrolysis cells (MECs) under thermophilic (70°C) and hypersaline (25% salinity) conditions. Of these, only the Valdivia brine pool produced high and consistent current 6.8±2.1A/m²-anode in MECs operated at a set anode potential of +0.2V vs. Ag/AgCl (+0.405V vs. standard hydrogen electrode). These results show that exoelectrogens are present in these extreme environments and can be used to startup MEC under thermophilic and hypersaline conditions. Bacteroides was enriched on the anode of the Valdivia MEC, but it was not detected in the open circuit voltage reactor seeded with the Valdivia brine pool.

A meta-analysis of soil salinization effects on nitrogen pools, cycles and fluxes in coastal ecosystems

Salinity intrusion caused by land subsidence resulting from increasing groundwater abstraction, decreasing river sediment loads and increasing sea level because of climate change has caused widespread soil salinization in coastal ecosystems. Soil salinization may greatly alter nitrogen (N) cycling in coastal ecosystems. However, a comprehensive understanding of the effects of soil salinization on ecosystem N pools, cycling processes and fluxes is not available for coastal ecosystems. Therefore, we compiled data from 551 observations from 21 peer-reviewed papers and conducted a meta-analysis of experimental soil salinization effects on 19 variables related to N pools, cycling processes and fluxes in coastal ecosystems. Our results showed that the effects of soil salinization varied across different ecosystem types and salinity levels. Soil salinization increased plant N content (18%), soil NH₄⁺ (12%) and soil total N (210%), although it decreased soil NO₃^- (2%) and soil microbial biomass N (74%). Increasing soil salinity stimulated soil N₂ O fluxes as well as hydrological NH₄⁺ and NO₂^- fluxes more than threefold, although it decreased the hydrological dissolved organic nitrogen (DON) flux (59%). Soil salinization also increased the net N mineralization by 70%, although salinization effects were not observed on the net nitrification, denitrification and dissimilatory nitrate reduction to ammonium in this meta-analysis. Overall, this meta-analysis improves our understanding of the responses of ecosystem N cycling to soil salinization, identifies knowledge gaps and highlights the urgent need for studies on the effects of soil salinization on coastal agro-ecosystem and microbial N immobilization. Additional increases in knowledge are critical for designing sustainable adaptation measures to the predicted intrusion of salinity intrusion so that the productivity of coastal agro-ecosystems can be maintained or improved and the N losses and pollution of the natural environment can be minimized.

A model on the biological treatment of saline wastewater

Water scarcity is not a new issue, neither is water pollution. While 70% of the earth’s surface is covered with water, only 3% of it is available as fresh water. Moreover the pollution of water resources has dramatically increased the problem of water scarcity over the last century. Bioremediation presents a cheap and effective solution of this problem. In particular, halophiles have been found to be effective in hypersaline wastewater treatment. Therefore, in this paper, we propose a nonlinear mathematical model to study the removal of a pollutant using halophiles in the hypersaline environment. The analysis of the model is being carried out using stability theory of differential equations. The results indicate that halophiles not only help in removing the organic pollutant, but also help in conversion of saline water into fresh water. The numerical simulations along with sensitivity analysis are performed to support the analytical results.

Physical-chemical evaluation of hydraulic fracturing chemicals in the context of produced water treatment

Produced water is a significant waste stream that can be treated and reused; however, the removal of production chemicals-such as those added in hydraulic fracturing-must be addressed. One motivation for treating and reusing produced water is that current disposal methods-typically consisting of deep well injection and percolation in infiltration pits-are being limited. Furthermore, oil and gas production often occurs in arid regions where there is demand for new water sources. In this paper, hydraulic fracturing chemical additive data from California are used as a case study where physical-chemical and biodegradation data are summarized and used to screen for appropriate produced water treatment technologies. The data indicate that hydraulic fracturing chemicals are largely treatable; however, data are missing for 24 of the 193 chemical additives identified. More than one-third of organic chemicals have data indicating biodegradability, suggesting biological treatment would be effective. Adsorption-based methods and partitioning of chemicals into oil for subsequent separation is expected to be effective for approximately one-third of chemicals. Volatilization-based treatment methods (e.g. air stripping) will only be effective for approximately 10% of chemicals. Reverse osmosis is a good catch-all with over 70% of organic chemicals expected to be removed efficiently. Other technologies such as electrocoagulation and advanced oxidation are promising but lack demonstration. Chemicals of most concern due to prevalence, toxicity, and lack of data include propargyl alcohol, 2-mercaptoethyl alcohol, tetrakis hydroxymethyl-phosphonium sulfate, thioglycolic acid, 2-bromo-3-nitrilopropionamide, formaldehyde polymers, polymers of acrylic acid, quaternary ammonium compounds, and surfactants (e.g. ethoxylated alcohols). Future studies should examine the fate of hydraulic fracturing chemicals in produced water treatment trains to demonstrate removal and clarify interactions between upstream and downstream processes.

Evaluating integrated strategies for robust treatment of high saline piggery wastewater

In this study, we integrated physicochemical and biological strategies for the robust treatment of piggery effluent in which high levels of organic constituents, inorganic nutrients, color, and salts remained. Piggery effluent that was stabilized in an anaerobic digester was sequentially coagulated, micro-filtered, and air-stripped prior to biological treatment with mixotrophic algal species that showed tolerance to high salinity (up to 4.8% as Cl(-)). The algae treatment was conducted with continuous O2 supplementation instead of using the combination of high lighting and CO2 injection. The microalga Scenedesmus quadricauda employed as a bio-agent was capable of assimilating both nitrogen (222 mg N g cell(-1) d(-1)) and phosphorus (9.3 mg P g cell(-1) d(-1)) and utilizing dissolved organics (2053 mg COD g cell(-1) d(-1)) as a carbon source in a single treatment process under the heterotrophic growth conditions. The heterotrophic growth of S. quadricauda proceeded rapidly by directly incorporating organic substrate in the oxidative assimilation process, which coincided with the high productivity of algal biomass, accounting for 2.4 g cell L(-1) d(-1). The algae-treated wastewater was subsequently ozonated to comply with discharge permits that limit color in the effluent, which also resulted in improved biodegradability of residual organics. The integrated treatment scheme proposed in this study also achieved 89% removal of COD, 88% removal of TN, and 60% removal of TP. The advantage of using the hybrid configuration suggests that this would be a promising strategy in full-scale treatment facilities for piggery effluent.

Biodegradation of direct blue 129 diazo dye by Spirodela polyrrhiza: An artificial neural networks modeling

Phytoremediation potential of the aquatic plant Spirodela polyrrhiza was examined for direct blue 129 (DB129) azo dye. The dye removal efficiency was optimized under the variable conditions of the operational parameters including removal time, initial dye concentration, pH, temperature and amount of plant. The study reflected the significantly enhanced dye removal efficiency of S. polyrrhiza by increasing the temperature, initial dye concentration and amount of plant. Intriguingly, artificial neural network (ANN) predicted the removal time as the most dominant parameter on DB129 removal efficiency. Furthermore, the effect of dye treatment on some physiologic indices of S. polyrrhiza including growth rate, photosynthetic pigments content, lipid peroxidation and antioxidant enzymes were studied. The results revealed a reduction in photosynthetic pigments content and in multiplication of fronds after exposure to dye solution. In contrast, malondialdehyde content as well as catalase (CAT) and peroxidase (POD) activities significantly increased that was probably due to the ability of plant to overcome oxidative stress. As a result of DB129 biodegradation, a number of intermediate compounds were identified by gas chromatography-mass spectroscopy (GC-MS) analysis. Accordingly, the probable degradation pathway of DB129 in S. polyrrhiza was postulated.

Use of a marine microbial community as inoculum for biomethane production

Marine substrates are prominent candidates for the production of biofuels, especially for biogas, which is a well-established technology that accepts different types of substrates for its production. However, the use of marine substrates in bioreactors may cause inhibition of methanogenic bacteria due to the addition of seasalts. Here, we explore a simple and economically viable way to circumvent the problem of inoculum inhibition. Based on the current knowledge of the diversity of microorganisms in marine sediments, we tested the direct use of methanogenic bacteria from an anoxic marine environment as inoculum for biomethane production. Both marine and freshwater substrates were added to this inoculum. No pretreatment (that may have enhanced methane production, but would have made the process more expensive) was applied either to the inoculum or to the substrates. For comparison, the same substrates were added to a standard inoculum (cow manure). Both the marine inoculum and cow manure produced methane by anaerobic digestion of the substrates added. The highest methane production (0.299 m(3) kg VS(-1)) was obtained by adding marine microalgae biomass (Chlorella sp. and Synechococcus sp.) to the marine inoculum. No inhibitory effects were observed due to differences in salinity between the inocula and substrates. Our results indicate the potential of using both marine inoculum and substrates for methane production.

Effects of salinity on performance and microbial community structure of an anoxic-aerobic sequencing batch reactor

The effects of salinity on the performance and microbial community structure of activated sludge were investigated in an anoxic-aerobic sequencing batch reactor (SBR). The removal efficiencies of chemical oxygen demand (COD) and [Formula: see text]-N decreased as the influent salinity increased from 0.5% to 6%. The specific oxygen utilization rate of activated sludge increased from 22.47 to 43.16 mg O2 g(-1) mixed liquid suspended solids (MLSS) h(-1) with the increase in salinity from 0.5% to 4% and subsequently decreased to 18.3 mg O2 g(-1) MLSS h(-1) at 6% salinity. The specific ammonium oxidation rate (SAOR) and specific nitrite oxidation rate (SNOR) decreased slowly at 0.5-1% salinity and then decreased rapidly with the increase in salinity from 1% to 6%. The SNOR diminished at a faster rate than the SAOR with the increase in salinity from 0.5% to 6%. The specific nitrate reduction rate (SNRR) decreased with the increase in salinity, whereas the SNRR was higher than the sum of SAOR and SNOR at 0.5-6% salinity. The denaturing gradient gel electrophoresis profiles revealed obvious changes in microbial community structure at different salinities. Some microbes were capable of tolerating up to 6% salinity in the SBR, such as Planomonospora sphaerica, Nitrosomonas sp. Is32, and Denitromonas sp. D2-1.

Evidence of glycoproteins and sulphated proteoglycan-like presence in extracellular polymeric substance from anaerobic granular sludge

The protein fraction of extracellular polymeric substance (EPS) from two anaerobic granular sludge samples was characterized with sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and a far western blotting method. SDS-PAGE was used with various staining applications to obtain a protein (silver), glycoprotein [periodic acid-Shiff's (PAS)] or proteoglycan-like (Alcian blue at pH 2.5 (carboxylic group) or 1 (sulphated group)) fingerprint. The fingerprints of the EPS denatured protein from the two sludge samples differed. Some proteins are specific to Soluble (S) or Bound (B)-EPS (20-100 kDa). Denatured proteins with a polysaccharide moieties characterization are more present in B-EPS. Glycoproteins with α-d-mannosyl and/or α-d-glucosyl (90, 50, 40 kDa) were detected. Proteoglycan-like and sulphated proteoglycan-like substances are also detected, mainly in B-EPS. A 68 kDa sulphated proteoglycan-like substance contains two glucidic residue types: α-d-mannosyl and/or α-d-glucosyl and N-acetyl-β-d-glucosamine. Such heteroproteins are present around the membrane as well as the surface-layer from Archaea and from some bacteria. The glycoprotein and sulphated proteoglycan-like substance are assumed to contribute to anaerobic granule strength, thanks to their ability to perform interactions of various nature (ionic, hydrophobic, Ca(2+) as divalent cation bridging, etc.).

Salt rejection and water flux through a tubular pervaporative polymer membrane designed for irrigation applications

The performance of a hydrophilic polyester tubular pervaporative membrane in treating high-salinity water for irrigation was investigated. The membrane was filled with contaminated water and placed in air, soil or sand media. When this occurs water diffuses through the tube, trapping salts within the tube. Sorption and permeation tests and scanning electron microscopy (SEM) were used to assess salt rejection and permeate flux through the tubular membrane when surrounded by deionized water, air, top soil or silver sand. Mean water uptake by the membrane was 0.5 L x m(-2) at room temperature and the water diffusion coefficient was 3.8 x 10(-4) cm2 x s(-1). The permeate flux across the membrane was 7.9 x 10(-3) L(m(-2) x h(-1)) in sand and 5.6 x 10(-2) in air. The rejection of sodium chloride by the tubular membrane in sand was 99.8% or above under all tested conditions. However, when the tube was filled with sodium chloride solution and placed in deionized water, salt was observed to permeate the membrane. SEM images confirmed that variable amounts of sodium chloride crystals were retained inside the membrane walls. These results support the potential application of such a tubular pervaporative membrane for irrigation applications using saline waters; however there may be reduced salt rejection under waterlogged soil conditions.

Fate and effect of xenobiotics on biodegradation processes: basis for respirometric appraisal

The paper mainly focused on illustrating the merit of respirometric analysis in assessing the inhibitory/toxic impact of xenobiotics on substrate biodegradation. It also evaluated biodegradation characteristics of these chemicals at continuous exposure through acclimation ofthe microbial culture. The nature and role ofoxygen uptake rate (OUR) profiles were discussed in conjunction with appropriate modelling, which should incorporate dissolved oxygen as an indispensable component for respirometric evaluation. Emphasis was placed upon differentiating acute effects from chronic impact, which may be totally different as it involves biodegradation of the chemical due biomass acclimation. Three case studies, each involving OUR measurements and process modelling, were presented for this purpose. The first one related to the inhibitory action of pharmaceutical effluent when mixed with plain-settled tannery wastewater. The second investigated the fate of H-acid, a commercially important naphthalene sulfonate, which exerted no adverse effect on substrate biodegradation, while remaining intact before and after a long acclimation period. The third one involved 2,6-dihydroxybenzoic acid, a naturally occurring organic compound in olive oil wastewater, which became biodegradable after acclimation by the development ofa specific microbial biomass fraction, while it heavily inhibited substrate biodegradation at first exposure. Model evaluation of the experimental data could provide related information on process stoichiometry and kinetics in all studies.

Growth kinetic models for phenol biodegradation in a batch culture of Pseudomonas putida

Biodegradation of phenol with pure culture of Pseudomonas putida was investigated. P. putida (PTCC 1694) was grown in facultative anaerobic condition at 27 degrees C and media pH value of 7. The effect of initial phenol concentration on the biodegradation rate was studied. The initial concentrations of phenol varied from 300 to 1000 mg/l. Experiments were performed for the duration of seven days while daily samples were withdrawn. The initial rate of biodegradation of phenol increased with initial concentration of 300-500 mg/l. Further increase in phenol concentration resulted in a slight decrease in the rate of biodegradation due to phenol inhibition. It was observed that by increasing the concentration of phenol, the lag phase was prolonged. Phenol is known to be an inhibitory substrate, thus Monod, Haldane and logistic kinetic models were applied to evaluate the growth kinetic parameters. The Monod model was unable to present the growth parameters over the defined concentration range. However, Haldane and logistic models perfectly fitted with the experimental data. The yield coefficients for the growth on phenol at concentrations of 300, 500, 700 and 1000 mg/l were 0.177, 0.062, 0.035 and 0.012 mg/mg, respectively.

Pollution profile and biodegradation characteristics of fur-suede processing effluents

This study investigated the effect of stream segregation on the biodegradation characteristics of wastewaters generated by fur-suede processing. It was conducted on a plant located in an organized industrial district in Turkey. A detailed in-plant analysis of the process profile and the resulting pollution profile in terms of significant parameters indicated the characteristics of a strong wastewater with a maximum total COD of 4285 mg L(-1), despite the excessive wastewater generation of 205 m3 (ton skin)(-1). Respirometric analysis by model calibration yielded slow biodegradation kinetics and showed that around 50% of the particulate organics were utilized at a rate similar to that of endogenous respiration. A similar analysis on the segregated wastewater streams suggested that biodegradation of the plant effluent is controlled largely by the initial washing/pickling operations. The effect of other effluent streams was not significant due to their relatively low contribution to the overall organic load. The respirometric tests showed that the biodegradation kinetics of the joint treatment plant influent of the district were substantially improved and exhibited typical levels reported for tannery wastewater, so that the inhibitory impact was suppressed to a great extent by dilution and mixing with effluents of the other plants. The chemical treatment step in the joint treatment plant removed the majority of the particulate organics so that 80% of the available COD was utilized in the oxygen uptake rate (OUR) test, a ratio quite compatible with the biodegradable COD fractions of tannery wastewater. Consequently, process kinetics and especially the hydrolysis rate appeared to be significantly improved.

Modelling the energy demands of aerobic and anaerobic membrane bioreactors for wastewater treatment

A modelling study has been developed in which the energy requirements of aerobic and anaerobic membrane bioreactors (MBRs) are assessed in order to compare these two wastewater treatment technologies. The model took into consideration the aeration required for biological oxidation in aerobic MBRs (AeMBRs), the energy recovery from methane production in anaerobic MBRs (AnMBRs) and the energy demands of operating submerged and sidestream membrane configurations. Aeration and membrane energy demands were estimated based on previously developed modelling studies populated with operational data from the literature. Given the difference in sludge production between aerobic and anaerobic systems, the model was benchmarked by assuming high sludge retention times or complete retention of solids in both AeMBRs and AnMBRs. Analysis of biogas production in AnMBRs revealed that the heat required to achieve mesophilic temperatures (35 degrees C) in the reactor was only possible with influent wastewater strengths above 4-5 g COD L(-1). The general trend of the submerged configuration, which is less energy intensive than the sidestream configuration in aerobic systems, was not observed in AnMBRs, mainly due to the wide variation in gas demand utilized in anaerobic systems. Compared to AeMBRs, for which the energy requirements were estimated to approach 2 kWh m(-3) (influent up to 1 g COD L(-1)), the energy demands associated with fouling control in AnMBRs were lower (0.80 kWh m(-3) for influent of 1.14 g COD L(-1)), although due to the low fluxes reported in the literature capital costs associated with membrane material would be three times higher than this.