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Microalgal-based bioprocess offers several advantages including wastewater reclamations, therefore present study assessed the usability of the combination of untreated municipal sewage wastewater (UTMSWW) and secondary treated municipal sewage wastewater (STSWW) for nutrient removal and recovery by

Microalgal-based bioprocess offers several advantages including wastewater reclamations, therefore present study assessed the usability of the combination of untreated municipal sewage wastewater (UTMSWW) and secondary treated municipal sewage wastewater (STSWW) for nutrient removal and recovery by Tetraselmis indica (T. indica) BDUG001. The present study optimized the additional nutrient supplementations (e.g. ASN-III) percentage and day-night cycle, pH and pH with aeration for monitoring high-rate biomass production and nutrient recovery. The study results showed that the combination of 75% UTMSWW + 25% ASN-III supported maximum biomass production (2.65 ± 0.07 g/L). In the optimized day-night cycle (12:12 h), T. indica BDUG001 showed improved biomass production (2.75 ± 0.07 g/L), biomass productivity (165.63 ± 4.42 mg/L/d), and photosynthetic pigments production. Under optimized pH∼ 7.0 with aeration, maximum total nitrate (TN) removal efficiency (87.67 ± 3.08–91.55 ± 1.92%) was observed, while COD and TP removal was maximum at pH ∼ 9.0. The maximum biomass production (2.35 ± 0.07–2.77 ± 0.04 g/L) with biomass productivity (93.75 ± 167.19 ± 2.21 mg/L/d) and lipid content (42.98 ± 1.86–47.85 ± 0.21% DCW) were also at pH 7.0. with aeration. The present study verified the utilization of UTMSWW with the combination of conventional medium, optimized day-night cycle, pH with aeration along with designing low-cost PBR. It was the ideal system for the cultivation of T. indica BDUG001 for the recovery of nutrients from wastewater, production of biofuels and value-added feedstock.

The major downfalls of the microalgal biorefinery are low volume of high value product accumulation, low biomass productivity and high cultivation costs. Here, we aimed to improve the biomass productivity of the industrially relevant

The bioremediation of emerging pollutants in wastewater via algal biotechnology has been emerging as a cost-effective and low-energy input technological solution. However, the algal bioremediation technology is still not fully developed at a commercial level. The development of different technologies and new strategies to cater specific needs have been studied. The existence of multiple emerging pollutants and the selection of microalgal species is a major concern. The rate of algal bioremediation is influenced by various factors, including accidental contaminations and operational conditions in the pilot-scale studies. Algal-bioremediation can be combined with existing treatment technologies for efficient removal of emerging pollutants from wastewater. This review mainly focuses on algal-bioremediation systems for wastewater treatment and pollutant removal, the impact of emerging pollutants in the environment, selection of potential microalgal species, mechanisms involved, and challenges in removing emerging pollutants using algal-bioremediation systems.

Manufacturing and resource industries are the key drivers for economic growth with a huge environmental cost (e.g. discharge of industrial effluents and post-mining substrates). Pollutants from waste streams, either organic or inorganic (e.g. heavy metals), are prone to interact with their physical environment that not only affects the ecosystem health but also the livelihood of local communities. Unlike organic pollutants, heavy metals or trace metals (e.g. chromium, mercury) are non-biodegradable, bioaccumulate through food-web interactions and are likely to have a long-term impact on ecosystem health. Microorganisms provide varied ecosystem services including climate regulation, purification of groundwater, rehabilitation of contaminated sites by detoxifying pollutants. Recent studies have highlighted the potential of methanotrophs, a group of bacteria that can use methane as a sole carbon and energy source, to transform toxic metal (loids) such as chromium, mercury and selenium. In this review, we synthesise recent advances in the role of essential metals (e.g. copper) for methanotroph activity, uptake mechanisms alongside their potential to transform toxic heavy metal (loids). Case studies are presented on chromium, selenium and mercury pollution from the tanneries, coal burning and artisanal gold mining, respectively, which are particular problems in the developing economy that we propose may be suitable for remediation by methanotrophs. Video Abstract Supplementary Information The online version contains supplementary material available at 10.1186/s40168-021-01112-y.

Tolypothrix, a self-flocculating, fast growing, CO

This study aimed to characterize the biofilm microbial community that causes corrosion of API 5LX carbon steel. API 5LX carbon steel coupons were incubated with raw produced water collected from two oil reservoir stations or filter-sterilized produced water. Biofilm 16S rRNA amplicon sequencing revealed that the bacterial community present in the biofilm was dominated by Proteobacteria, including Marinobacter hydrocarbonoclaustics and Marinobacter alkaliphilus. Electrochemical analysis such as impedance and polarization results indicated that Proteobacteria biofilm accelerated corrosion by ~ twofold (2.1 ± 0.61 mm/years) or ~ fourfold (~ 3.7 ± 0.42 mm/years) when compared to the control treatment (0.95 ± 0.1 mm/years). Scanning electron and atomic force microscopy revealed the presence of a thick biofilm and pitting corrosion. X-ray diffraction revealed higher amounts of the corrosion products Fe2O3, γ-FeOOH, and α-FeOOH, and confirmed that the microbial biofilm strongly oxidized the iron and contributed to the acceleration of corrosion of carbon metal API 5LX.

Methane (CH4), a highly reduced C1 compound, is one of the long-lived atmospheric gases with high global warming potential i.e., 28–36 times that of CO2 over 100 years. The atmospheric levels of CH4 reached ∼1863 part per billions (ppb) in 2014, and annual increase of atmospheric CH4 level thereafter measured as ∼10 ppb. The CH4 is projected to drive the rise in global temperature of ∼4–6◦C by 2050, and thus it is currently considered as the main target for global climate stabilization and mitigation (COP-21, 2015). Capturing anthropogenic CH4 to produce value products is highly feasible, but the great challenge is that to tap, concentrate, purify, store, transport, and utilize the CH4 from different point emission sources is presently not economically viable.

In present investigation, effect of diverting acidogenic off-gas from leached bed reactor (LBR) to up-flow anaerobic sludge blanket (UASB) reactor during semi-continuous food waste (FW) anaerobic digestion was evaluated. In test LBR headspace pressure (3.3 psi) was maintained with intermittent headspace gas transfer into UASB. In control, same headspace pressure was maintained without gas transfer. The semi-continuous FW addition affected the characteristics and production of leachate in control and test LBR. The cumulative COD, total soluble products and methane yields were 1.26, 1.37 and 3 times higher in the test LBR than the control. The acetate and methane yields from test LBR were 697.8 g.kgVSadded-1 and 167.55 mL.gCOD-1feeding. Acidogenic gas transfer maintained low partial pressure of hydrogen and the hydrogen to carbon-di-oxide ratio in the headspace of LBR, which were thermodynamically favorable for microbial metabolism and concomitant high-rate production of acetate-rich volatile fatty acid and methane-rich biogas from FW.

Anaerobic digestion of food waste (FW) requires external addition of buffer and/or trace metals, while co-digestion with complementary organic substrates such as sewage sludge is an alternative approach to overcome with the operational failures. In this batch study, co-digestion of chemically enhanced primary treated (CEPT) sludge mixed (mass to mass ratio) with FW in continuous stirred tank reactors (CSTR) was investigated. The total solid (TS) contents of the CSTR varied between 60 and 100 kg dm−3 were prepared by mixing FW:CEPT sludge (on wet weight basis) at ratios of 1:3, 1:5 and 1:7. In addition, ∼200 kg dm−3 inoculum was added to make up the total working volume in the CSTRs while contents were continuously mixed at 6.7 Hz and incubated at 35 °C for 20 days. Samples were collected intermittently from the CSTRs for the physiochemical analysis. The total biogas and methane (CH4) productions are reduced in all CSTRs within 7–10 days due to the accumulation of VFAs to inhibitory concentrations. The maximum CH4 production of 0.276 ± 0.02 dm3 kg−1 VS added was recorded for treatment with 1:7 mixing ratio with an acetic acid accumulation of 0.35 g g−1 (∼90% of total VFAs). The results suggested that the addition of FW in a sewage sludge digester will be beneficial to improve the CH4 recovery and provide an alternative mean for treating FW locally. However, the inoculum size and buffering requirements need to be critically analyzed during the continuous operations to avoid any process inhibition.

In present study, the efficiency of three oleaginous yeasts i.e., Yarrowia lipolytica, Rhodotorula glutinis and Cryptococcus curvatus were compared for their lipid assimilation capacities using three different FW-leachates as a medium. The FW-leachates were collected from dry anaerobic digesters and diluted to achieve carbohydrate content of 25gL-1 prior to yeast inoculations. Around 5% of yeast cultures were individually mixed in three different FW-leachate mediums and incubated under 30°C and 150rpm agitation for 6days. The Y. lipolytica produced high biomass with lipid contents of 49.0±2% on dry weight basis. Whereas, the acetic acid concentration of >6gL-1 inhibited the growth of R. glutinis. The study observed that the selection of appropriate FW-leachate composition is highly important for biolipid accumulation by oleaginous yeasts.

Tolypothrix, a self-flocculating, fast growing, CO2 and nitrogen-fixing cyanobacterium, can be cultivated in nutrient-poor ash dam waters of coal-fired power stations, converting CO2 emissions into organic biomass. Therefore, the biomass of Tolypothrix sp. is a promising source for bio-fertiliser production, providing micro- and macronutrients. Energy requirements for production could potentially be offset via anaerobic digestion (AD) of the produced biomass, which may further improve the efficiency of the resulting biofertilizer. The aim of this study was to evaluate the effectiveness of pre-treatment conditions and subsequent methane (CH4) production of Tolypothrix under out-door cultivation conditions. Pre-treatments on biogas and methane production for Tolypothrix sp. biomass investigated were: (1) thermal at 95 °C for 10 h, (2) hydrothermal by autoclave at 121 °C at 1013.25 hPa for 20 min, using a standard moisture-heat procedure, (3) microwave at an output power of 900 W and an exposure time of 3 min, (4) sonication at an output power of 10 W for 3.5 h at 10 min intervals with 20 s breaks and (5) freeze-thaw cycles at −80 °C for 24 h followed by thawing at room temperature. Thermal, hydrothermal and sonication pre-treatments supported high solubilization of organic compounds up to 24.40 g L−1. However, higher specific CH4 production of 0.012 and 0.01 L CH4 g−1 volatile solidsadded. was achieved for thermal and sonic pre-treatments, respectively. High N- and low C-content of the Tolypothrix biomass affected CH4 recovery, while pre-treatment accelerated production of volatile acids (15.90 g L−1) and ammonia-N-accumulation (1.41 g L−1), leading to poor CH4 yields. Calculated theoretical CH4 yields based on the elemental composition of the biomass were ~55% higher than actual yields. This highlights the complexity of interactions during AD which are not adequately represented by elemental composition.

Lignocellulose biomass is considered to be the prevalent and economic substrate for biofuel generation. The presence of certain refractory components in biomass causes major obstacle in enzymatic hydrolysis and thus it has to be improved by the advancement of pretreatment technology. The pretreatment focused on the enhancement of hydrolysis by altering the polymeric substance into monomers. A suitable pretreatment converts the biomass into easily accessible components for enzymes and thus enhances fermentation during biofuel production. Notwithstanding the research and development activities focused towards the goalmouth and the integrated pretreatment for biofuel production are needed to be optimised in terms of economic and environmental way. The problems associated with the economic and environmental distress focused on enormous research for several decades in order to replace fossil fuels with the lignocellulosic feedstock. The various approaches were implemented in lignocellulose based biofuel production by concerning the net cost and the energy demand by upgrading the process design. In present review, the pretreatment technologies for biofuel production from lignocellulosic feedstock are discussed along with the inhibitory compounds generations during pretreatment. Furthermore, the energy demand on pretreatment and the techno-economic and environmental aspects were discussed. This review highlights the major aspects in biorefinery process which includes the pretreatment and saccharification of sugar and lignin into biofuels.

Biorefining of second-generation feedstock gains more attention to improve the living standards and promote circular bioeconomy. The biorefinery concept made an effort to make the environmentally sustainable and economical products. Lignocellulosic biomass is widely available and extensively tested feedstock to produce biofuels, bioenergy and different value- products. By the integration of process to fractionate the lignin, cellulose and hemicellulose can add more values in the process chain that required integration and optimized technologies followed by life cycle analysis and economic assessment. The life cycle and economic analysis together assess the impacts on environment, economic and all the impacts which are involved indirectly throughout the product stages from cradle to grave. The improvement and integration of the current biorefinery process recommends the newer and sustainable bio-economy and will replace the fossil fuels with the renewable reserve. In techno-economic perspective, the optimization of integrated technologies for the production of biofuels and other bioproducts have still to be optimized for efficient production. The proper adoption of pretreatment methods increases the economic value in biorefinery process. The main aim of this review is to summarize the three key research areas that required more attentions, they are; (a) valorization of lignin, cellulose, hemicellulose into value added products, (b) integrated biorefinery approach and process optimization; and (c) circular bioeconomy and its future perspective. This review concludes that the lignocellulosic integrated biorefinery approach is feasible to support the circular bioeconomy, through which number of value products could be derived.

Methane mitigation in landfill top cover soils is mediated by methanotrophs whose optimal methane (CH4) oxidation capacity is governed by environmental and complex microbial community interactions. Optimization of CH4 remediating bio-filters need to take microbial responses into account. Divalent copper (Cu2+) and iron (Fe2+) are present in landfills at variable ratios and play a vital role in methane oxidation capacity and growth of methanotrophs. This study, as a first of its kind, therefore quantified effects of variable Cu2+ and Fe2+ (5:5, 5:25 and 5:50 μM) ratios on mixed methanotrophic communities enriched from landfill top cover (LB) and compost soils (CB). CH4 oxidation capacity, CH4 removal efficiencies, fatty acids content/profiles and polyhydroxybutyrate (PHB; a biopolymer) contents were also analysed to quantify performance and potential co-product development. Mixed methanotroph cultures were raised in 10 L continuous stirred tank reactors (CSTRs, Bioflo® & Celligen® 310 Fermentor/Bioreactor; John Morris Scientific, Chatswood, NSW, Australia). Community structure was determined by amplifying the V3-V4 region of 16s rRNA gene. Community structure and, consequently, fatty acid-profiles changed significantly with increasing Cu2+/Fe2+ ratios, and responses were different for LB and CB. Effects on methane oxidation capacities and PHB content were similar in the LB- and CB-CSTR, decreasing with increasing Cu2+/Fe2+ ratios, while biomass growth was unaffected. In general, high Fe2+ concentration favored growth of the type -II methanotroph Methylosinus in the CB-CSTR, but methanotroph abundances decreased in the LB-CSTR. Increase in Cu2+/Fe2+ ratio increased the growth of Sphingopyxis in both systems, while Azospirllum was co-dominant in the LB- but absent in the CB-CSTR. After 13 days, methane oxidation capacities and PHB content decreased by ∼50% and more in response to increasing Fe2+ concentrations. Although methanotroph abundance was ∼2% in the LB- (compared to >50% in CB-CSTR), methane oxidation capacities were comparable in the two systems, suggesting that methane oxidation capacity was maintained by the dominant Azospirllum and Sphingopyxis in the LB-CSTR. Despite similar methanotroph inoculum community composition and controlled environmental variables, increasing Cu2+/Fe2+ ratios resulted in significantly different microbial community structures in the LB- and CB-CSTR, indicative of complex microbial interactions. In summary, our results suggest that a detailed understanding of allelopathic interactions in mixed methanotrophic consortia is vital for constructing robust bio-filters for CH4 emission abatement.

The present study evaluates, the oxidation behaviour of thermophilic bacteria Geobacillus thermoparaffinivorans IR2, Geobacillus stearothermophillus IR4 and Bacillus licheniformis MN6 on carbon steel API 5 LX by weight loss, electrochemical studies (impedance and polarization analysis) and surface analysis (X-ray diffraction spectroscopy). The presence of IR2, IR4 and MN6 showed highest corrosion rate (CR) of 2.51, 2.82 and 2.41 mm/year, respectively, than the abiotic control (0.95 mm/year). Whereas in the presence of biocide tetrakis (hydroxymethyl) phosphonium sulphate (THPS) inhibition of the biofilm formation was noticed on the carbon steel and thus reduced the CR of about 0.36, 0.46 and 0.42 mm/year. The electrochemical studies also revealed that higher charge transfer resistance (105 Ω cm2) and solution resistance (6.99 Ω cm2) in the presence of THPS due to the intact protective film on carbon steel surface. Thus, THPS is found to act as an effective candidate towards control microbial influenced corrosion by thermophilic bacteria on carbon steel API5LX in a 36% chloride environment.

Plastics are an indispensable part of day-to-day life. Environmental implications of these non-biodegradable plastics in landfills raise major concerns. Use of biodegradable plastics is the best alternative as they are environmental friendly, with great recycling potential, and can be produced using renewable resources such as waste materials, methane (CH4) and simple carbon sources. Whilst the biodegradable plastics are eco-friendly, they pose a risk of emitting CH4 under anaerobic conditions in landfills. As a cradle-to-cradle approach, landfill CH4 could be effectively used for biodegradable plastic production by methanotrophs. This review briefly reviews approaches to plastic disposal, alternatives to plastic waste management and outlines issues arising. The focus of the review is to examine the potential for cost-effective production of polyhydroxybutyrate (PHB) using methanotrophs for manufacturing biodegradable plastics. The data input into this analysis is derived from Australian landfill CH4 emissions, the average PHB content of methanotrophs and applied to a case-scenario in Sydney, Australia.. The results suggest that this approach to biodegradable plastic production can be economically viable and price-competitive with synthetic plastics. In our case study, landfills were sized small, medium and large (5,000, 35,000 and 230,000 t of waste per year, respectively). In small landfills, 162 t of CH4 can be recovered to produce 71 t of PHB per year, whilst in large landfills 7,480 t of CH4 can be recovered to produce 3,252 t of PHB. The cost of PHB production can be reduced to 1.5–2.0 AUD meeting the market value of synthetic plastic by increasing production volumes through building a centralised extraction and refinement facility suitable for large metropolitan cities.

Biotechnological production of vanillin is gaining momentum as the natural synthesis of vanillin that is very expensive. Ferulic acid (FA), a costly compound, is used as the substrate to produce vanillin biotechnologically and the making process is still expensive. Therefore, this study investigated the practical use of an agrobiomass waste, rice bran, and provides the first evidence of a cost-effective production of vanillin within 24 h of incubation using recombinant Pediococcus acidilactici BD16 (fcs +/ech +). Introduction of two genes encoding feruloyl CoA synthetase and enoyl CoA hydratase into the native strain increased vanillin yield to 4.01 g L−1. Bioconversion was monitored through the transformation of phenolic compounds. A hypothetical metabolic pathway of rice bran during the vanillin bioconversion was proposed with the inserted pathway from ferulic acid to vanillin and compared with that of other metabolic engineered strains. These results could be a gateway of using recombinant lactic acid bacteria for industrial production of vanillin from agricultural waste.

This study investigated hydrolysis approaches for cultivation of the oleaginous red yeast Rhodotorula glutinis for biodiesel production, whilst utilising the residual solids (RS) for biogas production. Macerated fruit and vegetable waste (FVW) (24h-4°C-leachate served as the control, Pcon) was hydrolysed chemically (Chem), thermally (Therm) and using a combined thermo-chemical treatment (T-Chem). All cleared hydrolysates supported growth of R. glutinis, which was nitrogen-limited. T-Chem hydrolysates yielded highest biomass, total fatty acids (TotFA) and RS-derived biogas yields, biomass TotFA failed to meet standards for fuel density and higher heating values, met by the other treatments. Even though Pcon-derived yields were slightly lower, it is recommended for FVW treatment for local biogas and biodiesel production due to energy and environmental impact considerations.

Composting of pig manure is a challenging task that requires appropriate co-substrate and bulking agent to provide optimum composting conditions and reduce nitrogen loss. In this study, paper waste is co-composted with pig manure as well as wood chips as the bulking agents. These raw materials were mixed at three different ratios of paper: pig manure: wood chips = 1:1:0 (pile 1), 3:2:1 (pile 2) and 3:1:1(pile 3), respectively. Each composting pile was about 11 m3 in size equipped with negative-pressure forced aeration. The temperature of all the three piles ranged between 43 and 76°C and therefore produced pathogen-free compost. The overall total carbon reduction of 39%, 36% and 36% were achieved from pile 1, 2 and 3, respectively. The increased with the composting period, indicating the transformation of ammoniacal-N into nitrate by nitrification activity. However, all three piles showed significant variations in soluble at different stages of composting, which could be due to the microbial assim...

The use of conventional continuous stirred tank reactor (CSTR) can affect the methane (CH4) recovery in a two-stage anaerobic digestion of food waste (FW) due to carbon short circuiting in the hydrolysis-acidogenesis (Hy-Aci) stage. In this research, we have designed and tested a solid-liquid-separating CSTR (SLS-CSTR) for effective Hy-Aci of FW. The working conditions were pH 6 and 9 (SLS-CSTR-1 and -2, respectively); temperature-37°C; agitation-300rpm; and organic loading rate (OLR)-2gVSL(-1)day(-1). The volatile fatty acids (VFA), enzyme activities and bacterial population (by qPCR) were determined as test parameters. Results showed that the Hy-Aci of FW at pH 9 produced ∼35% excess VFA as compared to that at pH 6, with acetic and butyric acids as major precursors, which correlated with the high enzyme activities and low lactic acid bacteria. The design provided efficient solid-liquid separation there by improved the organic acid yields from FW.

Understanding the role of heterotrophic-methanotrophic (H-Meth) communities is important for improvement of methane (CH4) oxidation capacities (MOC) particularly in conjunction with bio-product development in industrial bio-filters. Initially, a H-Meth consortium was established and enriched from marine sediments and characterized by next generation sequencing of the 16s rDNA gene. The enriched consortium was subjected to 10-50% CH4 (i.e., 0.20-1.6 CH4/O2 ratios) to study the effects on MOCs, biomass growth, fatty acid profiles and biopolymer (e.g. polyhydroxybutyrate; PHB) content. Methylocystis, Methylophaga and Pseudoxanthomonas dominated the H-Meth consortium. Culture enrichment of the H-Meth consortium resulted in 15-20-folds higher MOC compared to seed sediments. Increasing CH4 concentration (and decreased O2 levels) yielded higher MOCs, but did not improve total fatty acid contents. PHB contents varied between 2.5% and 8.5% independently of CH4/O2 ratios. The results suggest that H-Meth consortia could potentially be used in industrial bio-filters for production of biopolymer/biofuel precursors from CH4.

Potential of methane production by co-digestion of food waste with saline sludge produced from sewage receiving seawater toilet flushing was investigated to determine its suitability for food waste management in Hong Kong by making use of excess design capacity of sludge digesters. High salinity of saline sludge (12.8 mS/cm) affected degradation of organic compounds resulting in an increase in sCOD by 135% as compared to an increase by 283% in treatments with non-saline sludge (4.2 mS/cm) co-digestion. This inhibitory effect was also evident by lower VS removal efficiency of 32.65% for saline versus 54.23% for non-saline sludge based co-digestion. Furthermore, non-saline sludge gave a 3.4-fold higher methane yield than saline sludge co-digestion. It is concluded that co-digestion of food waste with both sludges could be adopted as a potential strategy to make use of excess digestion capacity of existing wastewater treatment facilities but is more viable for non-saline sludge.