Effect of iron sources on methane production and phosphorous transformation in an anaerobic digestion system of waste activated sludge.

The iron materials are commonly employed to enhance resource recovery from waste activated sludge through anaerobic digestion (AD). The influence of different iron sources, such as Fe2O3, Fe3O4, and FeCl3 on methane production and phosphorus transformation in AD systems with thermal hydrolyzed sludge as the substrate was assessed in this study. The results indicated that iron oxides effectively promote methane yield and methane production rate in AD systems, resulting in a maximum increase in methane production by 1.6 times. Soluble FeCl3 facilitated the removal of 92.3% of phosphorus from the supernatant through the formation of recoverable precipitates in the sludge. The introduction of iron led to an increase in the abundance of bacteria responsible for hydrolysis and hydrogenotrophic methanogenesis. However, the enrichment of microbial communities varied depending on the specific irons used. This study provides support for AD systems that recover phosphorus and produce methane efficiently from waste sludge.

Neuro-fuzzy modelling of a continuous stirred tank bioreactor with ceramic membrane technology for treating petroleum refinery effluent: a case study from Assam, India.

A continuous stirred tank bioreactor (CSTB) with cell recycling combined with ceramic membrane technology and inoculated with Rhodococcus opacus PD630 was employed to treat petroleum refinery wastewater for simultaneous chemical oxygen demand (COD) removal and lipid production from the retentate obtained during wastewater treatment. In the present study, the COD removal efficiency (CODRE) (%) and lipid concentration (g/L) were predicted using two artificial intelligence models, i.e., an artificial neural network (ANN) and a neuro-fuzzy neural network (NF-NN) with a network topology of 6-25-2 being the best for NF-NN. The results revealed the superiority of NF-NN over ANN in terms of determination coefficient (R2), root mean square error (RMSE), and mean absolute percentage error (MAPE). Three learning algorithms were tested with NF-NN; among them, the Bayesian regularization backpropagation (BR-BP) outperformed others. The sensitivity analysis revealed that, if solid retention time and biomass concentrations were maintained between 35 and 75 h and 3.0 g/L and 3.5 g/L, respectively, high CODRE (93%) and lipid concentration (2.8 g/L) could be obtained consistently.

Odor and volatile organic compounds biotreatment using compact trickle bed bioreactors (CTBB) in a wastewater treatment plant.

The main aim of this study was to optimize and maximize the impacts of odor and volatile organic compounds (VOCs) biodegradation in a wastewater treatment plant utilizing a pilot-scale compact trickle bed bioreactor (CTBB). A CTBB was built and tested for its long-term performance during which gases were supplied from the tank containing semi-liquid fats, oils, and fat waste. The concentrations of pollutants ranged from 0 to 140.75 mg/m3 H2S, 0 to 2500 mg/m3 VOCs, and 0 to 21.5 mg/m3 NH3. The CTBB was tested at different gas flow rates and at two pH values for the liquid phase: pH = 7.0 and 5.0. In the liquid phase, the pollutant removal efficiency was higher at pH = 7.0 than at pH = 5.0. Overall, the removal efficiency was between 81.5 % and 99.5 % for the VOCs and 87.5 % and 98.9 % for H2S, while NH3 removals were >99 %.

Performance and neural modeling of a compost-based biofilter treating a gas-phase mixture of benzene and xylene.

Biofilter (BF) has been regarded as a versatile gas treatment technology for removing volatile organic compounds (VOCs) from contaminated gas streams. In order for BF to be utilized in the industrial setting, it is essential to conduct research aimed at removing VOC mixtures under different inlet loading conditions, i.e. as a function of the gas flow rate and inlet VOC concentrations. The main aim of this study was to apply artificial neural networks (ANN) and determine the relationship between flow rate (FR), pressure drop (PD), inlet concentration (C), and removal efficiency (RE) in the BF treating gas-phase benzene and xylene mixtures. The ANN model was trained and tested to assess the removal efficiency of benzene (REB) and xylene (REX) under the influence of different FR, PD and C. The model's performance was assessed using a cross-validation method. The REb varied from 20% to >60%, while the REx varied from 10% to 70% during the different experimental phases of BF operation. The causal index (CI) technique was used to determine the sensitivity of the input parameters on the output variables. The ANN model with a topology of 4-4-2 performed the best in terms of predicting the RE profiles of both the pollutants. Furthermore, the effect was more pronounced for xylene because an increase in the benzene concentration reduced xylene removal (CI = -25.7170) more severely than benzene removal. An increase in the xylene concentration had a marginally positive effect on the benzene removal (CI = +0.1178).

Valorization of wastewater to recover value-added products: A comprehensive insight and perspective on different technologies.

In recent years, due to rapid globalization and urbanization, the demand for fuels, energy, water and nutrients has been continuously increasing. To meet the future need of the society, wastewater is a prominent and emerging source for resource recovery. It provides an opportunity to recover valuable resources in the form of energy, fertilizers, electricity, nutrients and other products. The aim of this review is to elaborate the scientific literature on the valorization of wastewater using wide range of treatment technologies and reduce the existing knowledge gap in the field of resource recovery and water reuse. Several versatile, resilient environmental techniques/technologies such as ion exchange, bioelectrochemical, adsorption, electrodialysis, solvent extraction, etc. are employed for the extraction of value-added products from waste matrices. Since the last two decades, valuable resources such as polyhydroxyalkanoate (PHA), matrix or polymers, cellulosic fibers, syngas, biodiesel, electricity, nitrogen, phosphorus, sulfur, enzymes and a wide range of platform chemicals have been recovered from wastewater. In this review, the aspects related to the persisting global water issues, the technologies used for the recovery of different products and/or by-products, economic sustainability of the technologies and the challenges encountered during the valorization of wastewater are discussed comprehensively.

Uncovering the phytochemicals of root exudates and extracts of lead (Pb) tolerant Chrysopogon zizanioides (L.) Roberty in response to lead contamination and their effect on the chemotactic behavior of rhizospheric bacteria.

The chemical composition of root exudates and root extracts from Chrysopogon zizanioides (L.) Roberty cv KS-1 was determined in the presence of lead [Pb(II)]. Hitherto, no information is available in the literature concerning the phytochemical components of root exudates of C. zizanioides. Significantly higher concentrations of total carbohydrates (26.75 and 42.62% in root exudates and root extract, respectively), reducing sugars (21.46 and 56.11% in root exudates and root extract, respectively), total proteins (9.22 and 23.70% in root exudates and root extract, respectively), total phenolic acids (14.69 and 8.33% in root exudates and root extract, respectively), total flavonoids (14.30 and 12.28% in root exudates and root extract, respectively), and total alkaloids (12.48 and 7.96% in root exudates and root extract, respectively) were observed in samples from plants growing under Pb(II) stress in comparison to the respective controls. GC-MS profiling showed the presence of a diverse group of compounds in root exudates and extracts, including terpenes, alkaloids, flavonoids, carotenoids, plant hormones, carboxylic/organic acids, and fatty acids. Among the detected compounds, many have an important role in plant development, regulating rhizosphere microbiota and allelopathy. Furthermore, the results indicated that C. zizanioides exudates possess a chemotactic response for rhizospheric bacterial strains Bacillus licheniformis, Bacillus subtilis, and Acinetobacter junii Pb1.

Wastewater in the food industry: Treatment technologies and reuse potential.

Water is the most extensively used raw material in the food and beverage industry. This industrial sector has a negative impact on the environment and economy as a result of rising water demand and wastewater production. With the increasing scarcity of drinking water, the reuse of wastewater streams has become an important economic and ecological concern. Therefore, the optimisation of water consumption and wastewater reuse in the food industry is essential. On the other hand, several countries limit the reuse of wastewater because of legal curtailment, public health and safety concerns. This represents a major challenge for both industries and administrations due to the technical complexity and financial costs involved. The present review aims at addressing the key issues related to water consumption, wastewater generation, treatment and successful implementation cases of water reuse in the food and beverage industry. Moreover, the various case studies of already employed technologies for the food industry wastewater treatment and reuse have been analysed for their performance. Also, this review reveals future research on the application of other innovative technologies such as ultraviolet irradiation and micro electrolysis. However, the successful implementation of reuse strategies is associated with the holistic evaluation of local factors such as governmental incentives, social acceptance and legislation harmonisation related to the cost, risks, and environmental performance.

Palm oil industrial wastes as a promising feedstock for biohydrogen production: A comprehensive review.

By the year 2050, it is estimated that the demand for palm oil is expected to reach an enormous amount of 240 Mt. With a huge demand in the future for palm oil, it is expected that oil palm by-products will rise with the increasing demand. This represents a golden opportunity for sustainable biohydrogen production using oil palm biomass and palm oil mill effluent (POME) as the renewable feedstock. Among the different biological methods for biohydrogen production, dark fermentation and photo-fermentation have been widely studied for their potential to produce biohydrogen by using various waste materials as feedstock, including POME and oil palm biomass. However, the complex structure of oil palm biomass and POME, such as the lignocellulosic composition, limits fermentable substrate available for conversion to biohydrogen. Therefore, proper pre-treatment and suitable process conditions are crucial for effective biohydrogen generation from these feedstocks. In this review, the characteristics of palm oil industrial waste, the process used for biohydrogen production using palm oil industrial waste, their pros and cons, and the influence of various factors have been discussed, as well as a comparison between studies in terms of types of reactors, pre-treatment strategies, the microbial culture used, and optimum operating condition have been presented. Through biological production, hydrogen production rates up to 52 L-H2/L-medium/h and 6 L-H2/L-medium/h for solid and liquid palm oil industrial waste, respectively, can be achieved. In short, the continuous supply of palm oil production by-product and relatively, the low cost of the biological method for hydrogen production indicates the potential source of renewable energy.

Effect of tungsten and selenium on C1 gas bioconversion by an enriched anaerobic sludge and microbial community analysis.

The effect of trace metals, namely tungsten and selenium, on the production of acids and alcohols through gas fermentation by a CO-enriched anaerobic sludge in a continuous gas-fed bioreactor was investigated. The CO-enriched sludge was first supplied with a tungsten-deficient medium (containing selenium) and in a next assay, a selenium-deficient medium (containing tungsten) was fed to the bioreactor, at a CO gas flow rate of 10 mL/min. In the absence of tungsten (tungstate), an initial pH of 6.2 followed by a pH decrease to 4.9 yielded 7.34 g/L acetic acid as the major acid during the high pH period. Subsequently, bioconversion of the acids at a lower pH of 4.9 yielded only 1.85 g/L ethanol and 1.2 g/L butanol in the absence of tungsten (tungstate). A similar follow up assay in the same bioreactor with two consecutive periods at different pH values (i.e., 6.2 and 4.9) with a selenium deficient medium yielded 6.6 g/L acetic acid at pH 6.2 and 4 g/L ethanol as well as 1.88 g/L butanol at pH 4.9. The results from the microbial community analysis showed that the only known CO fixing microorganism able to produce alcohols detected in the bioreactor was Clostridium autoethanogenum, both in the tungsten and the selenium deprived media, although that species has so far not been reported to be able to produce butanol. No other solventogenic acetogen was detected.

Reduction of selenite to elemental Se(0) with simultaneous degradation of phenol by co-cultures of Phanerochaete chrysosporium and Delftia lacustris.

The simultaneous removal of phenol and selenite from synthetic wastewater was investigated by adopting two different co-culturing techniques using the fungus Phanerochaete chrysosporium and the bacterium Delftia lacustris. Separately grown biomass of the fungus and the bacterium (suspended co-culture) was incubated with different concentrations of phenol (0-1,200 mg/L) and selenite (10 mg/L). The selenite ions were biologically reduced to extracellular Se(0) nanoparticles (3.58 nm diameter) with the simultaneous degradation of up to 800 mg/L of phenol. Upon growing the fungus and the bacterium together using an attached growth co-culture, the bacterium grew as a biofilm onto the fungus. The extracellularly produced Se(0) in the attached growth co-culture had a minimum diameter of 58.5 nm. This co-culture was able to degrade completely 50 mg/L phenol, but was completely inhibited at a phenol concentration of 200 mg/L.

Application of a compact trickle-bed bioreactor for the removal of odor and volatile organic compounds emitted from a wastewater treatment plant.

A compact trickle-bed bioreactor (CTBB) was tested for the removal of volatile organic compounds (VOCs) and hydrogen sulphide (H2S) present in the exhaust air of a wastewater treatment plant. At gas-flow rates varying between 2.0 and 30.0 m3/h and for specific pollutant loads up to 20 g/(m3·h), removal efficiencies for H2S and VOC were >95%. The CTBB was designed for a maximum H2S concentration of ∼200 ppm and removal efficiencies >97% were noticed. VOC concentrations were in the range of 25-240 ppmv and the removal efficiency was in the range of 85-99%. Possible consequences of an excessive pollutant overload and the time required for regenerating the microbial activity and reviving stable process conditions in the CTBB were also investigated. An increase in the H2S concentration from 400 to 600 ppmv for a few hours caused bioreactor poisoning; however, when original H2S concentrations were restored, stable CTBB operation was ascertained within 3 h.

Periphytic biofilms: A promising nutrient utilization regulator in wetlands.

Low nutrient utilization efficiency in agricultural ecosystems is the main cause of nonpoint source (NPS) pollution. Therefore, novel approaches should be explored to improve nutrient utilization in these ecosystems. Periphytic biofilms composed of microalgae, bacteria and other microbial organisms are ubiquitous and form a 'third phase' in artificial wetlands such as paddy fields. Periphytic biofilms play critical roles in nutrient transformation between the overlying water and soil/sediment, however, their contributions to nutrient utilization improvement and NPS pollution control have been largely underestimated. This mini review summarizes the contributions of periphytic biofilms to nutrient transformation processes, including assimilating and storing bioavailable nitrogen and phosphorus, fixing nitrogen, and activating occluded phosphorus. Future research should focus on augmenting the nitrogen fixing, phosphate solubilizing and phosphatase producing microorganisms in periphytic biofilms to improve nutrient utilization and thereby reduce NPS pollution production in artificial and natural wetland ecosystems.

Accumulation efficiency, genotoxicity and antioxidant defense mechanisms in medicinal plant Acalypha indica L. under lead stress.

The present study was designed to assess the physiological and biochemical changes in roots and shoots of the herb Acalypha indica grown under hydroponic conditions during exposure to lead (Pb) (100-500 mg L-1) for 1-12 d. The accumulation of Pb by A. indica plants was found to be 121.6 and 17.5 mg g-1 dry weight (DW) in roots and shoots, respectively, when exposed to a Pb concentration of 500 mg L-1. The presence of Pb ions in stem, root and leaf tissues was confirmed by scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDX) analyses. Concerning the activity of antioxidant enzymes, viz., peroxidase (POX) catalase (CAT) and ascorbate peroxidase (APX), they were induced at various regimes during 5, 8 and 12 d of Pb exposure in both the leaves and roots than untreated controls. Lead treatment increased superoxide dismutase (SOD) activity in both the leaf and root tissues over control, irrespective of the duration of exposure. Anew, it was observed that Pb treatments induced variations in the number and intensity of protein bands. Random amplified polymorphic DNA (RAPD) results show that the Pb treatment caused genotoxicity on DNA molecules as evidenced by the amplification of new bands and the absence of normal DNA amplicons in treated plants. Results confirm that A. indica is a Pb accumulator species, and the antioxidants might play a crucial role in the detoxification of Pb-induced toxic effects.

Sorption of zinc onto elemental selenium nanoparticles immobilized in Phanerochaete chrysosporium pellets.

The use of a novel hybrid biosorbent, elemental selenium nanoparticles (nSe0) immobilized in pellets of Phanerochaete chrysosporium, to remove Zn from aqueous solutions was investigated. Fungal pellets containing nSe0 (nSe0-pellets) showed to be better biosorbents as they removed more Zn (88.1 ± 5.3 %) compared to Se-free fungal pellets (56.2 ± 2.8 %) at pH 4.5 and an initial Zn concentration of 10 mg L-1. The enhanced sorption capacity of nSe0-pellets was attributed to a higher concentration of sorption sites resulting in a more negative surface charge density, as determined by analysis of the potentiometric titration data. Fourier transform infrared spectroscopy (FT-IR) analysis of fungal pellets prior to and after being loaded with Zn showed the functional groups, including hydroxyl and carboxyl groups, involved in the sorption process. The experimental data indicated that the sorption rate of the nSe0-pellets fitted well to the pseudo-second order kinetic model (R 2  = 0.99), and the sorption isotherm was best represented by the Sips model (Langmuir-Freundlich) with heterogeneous factor n = 1 (R 2  = 0.99), which is equivalent to the Langmuir model. Operational advantages of fungal pelleted reactors and the Zn removal efficiencies achieved by nSe0-pellets under mild acidic conditions make nSe0-pellet based bioreactors an efficient biosorption process.

Effect of temperature on selenium removal from wastewater by UASB reactors.

The effect of temperature on selenium (Se) removal by upflow anaerobic sludge blanket (UASB) reactors treating selenate and nitrate containing wastewater was investigated by comparing the performance of a thermophilic (55 °C) versus a mesophilic (30 °C) UASB reactor. When only selenate (50 µM) was fed to the UASB reactors (pH 7.3; hydraulic retention time 8 h) with excess electron donor (lactate at 1.38 mM corresponding to an organic loading rate of 0.5 g COD L(-1) d(-1)), the thermophilic UASB reactor achieved a higher total Se removal efficiency (94.4 ± 2.4%) than the mesophilic UASB reactor (82.0 ± 3.8%). When 5000 µM nitrate was further added to the influent, total Se removal was again better under thermophilic (70.1 ± 6.6%) when compared to mesophilic (43.6 ± 8.8%) conditions. The higher total effluent Se concentration in the mesophilic UASB reactor was due to the higher concentrations of biogenic elemental Se nanoparticles (BioSeNPs). The shape of the BioSeNPs observed in both UASB reactors was different: nanospheres and nanorods, respectively, in the mesophilic and thermophilic UASB reactors. Microbial community analysis showed the presence of selenate respirers as well as denitrifying microorganisms.

Start-up, performance and optimization of a compost biofilter treating gas-phase mixture of benzene and toluene.

The performance of a compost biofilter inoculated with mixed microbial consortium was optimized for treating a gas-phase mixture of benzene and toluene. The biofilter was acclimated to these VOCs for a period of ∼18d. The effects of concentration and flow rate on the removal efficiency (RE) and elimination capacity (EC) were investigated by varying the inlet concentration of benzene (0.12-0.95g/m(3)), toluene (0.14-1.48g/m(3)) and gas-flow rate (0.024-0.072m(3)/h). At comparable loading rates, benzene removal in the mixture was reduced in the range of 6.6-41% in comparison with the individual benzene degradation. Toluene removal in mixture was even more affected as observed from the reductions in REs, ranging from 18.4% to 76%. The results were statistically interpreted by performing an analysis of variance (ANOVA) to elucidate the main and interaction effects.