Pretreatment Of Wastewater Research Articles

Pilot-scale study on an advanced Fe-Cu process for refractory wastewater pretreatment

The extreme pH, high color, and poor biodegradability of refractory wastewater have severe impacts on its biological treatment. To address this issue, an advanced Fe-Cu process with redox reaction and spontaneous coagulation was investigated and applied for pilot-scale (wastewater flow rate of 2000 m3·day−1) pretreatment of separately discharged acidic chemicals and alkaline dyeing wastewater. The advanced Fe-Cu process had five functions: (1) increasing the pH of chemical wastewater to 5.0 and above, with an influent pH of approximately 2.0; (2) transforming refractory organics of chemical wastewater with 10.0% chemical oxygen demand (COD) and 30.8% color removal, thereby enhancing the ratio of biological oxygen demand after five days (BOD5) to COD (B/C) from 0.21 to 0.38; (3) neutralizing the pH of the pretreated chemical wastewater for coagulation application with alkaline dyeing wastewater to avoid adding alkaline chemical; (4) achieving average nascent Fe(II) concentrations of 925.6 mg∙L−1 using Fe-Cu internal electrolysis for mixed wastewater coagulation, resulting in an average of 70.3% color removal and 49.5% COD removal; (5) providing more efficient COD removal and B/C enhancement than FeSO4∙7 H2O coagulation while avoiding secondary pollution. The green process offers an effective, easy-implemented solution for the pretreatment of separately discharged acidic and alkaline refractory wastewater.

The Treatment of Aquaculture Wastewater with Biological Aerated Filters: From the Treatment Process to the Microbial Mechanism

Algal cell proliferation has posed significant problems for traditional water treatment facilities; these problems are attributed to surface hydrophilicity and electrostatic repulsion. Biological aerated filters (BAFs) have been extensively used in wastewater treatment to remove pollutants such as algal cells by utilizing the adsorption and separation capabilities of the filter media. In this study, a BAF was supplemented with biological filter medium (Marchantia polymorpha) to assess its effectiveness of pretreating aquaculture wastewater. In terms of process performance, steady and consistent treatment was achieved by the BAF with M. polymorpha (BAF2) under an algal cell density as high as 1.65 × 108 cell/L, with average removal rates for NH4+-N and algae cells of 74.4% and 81.9%, respectively. The photosynthetic activity parameters (rETRmax, α, Fv/Fm, and Ik) of the influent and effluent were quantitatively assessed, and M. polymorpha was found to remove algae by disrupting the photosynthetic system of the algal cells. Furthermore, the addition of the M. polymorpha filter medium enhanced the community structure of the functional microbes in the BAF system. The highest microbial community richness and diversity were observed in the BAF2. Meanwhile, M. polymorpha promoted an increase in the abundance of denitrifying bacteria, including Bdellovibrio and Pseudomonas. Overall, this work offers a unique perspective on the aquaculture wastewater pretreatment process and BAF design.

Sonophotocatalytic Degradation of Fast Yellow AB and Remazol Brilliant Violet-5R by Using Ag-Impregnated ZnO as a Photocatalyst.

The fundamental aim of this project was to assess the sonophotocatalytic degradation of textile dyes mostly eluted from industries into wastewater. Such a pretreatment of wastewater makes the water suitable for drinking and irrigation purposes and thereby helps protect the ecosystem. The main objective of this research was to degrade real samples and laboratory-prepared samples sonophotocatalytically using a silver-impregnated ZnO photocatalyst. Reactive dyes, including Fast Yellow AB (FY AB) and Remazol Brilliant Violet-5R (RBV-5R), were degraded via this technique under optimum and enhanced conditions. The photocatalyst was synthesized through a wet impregnation process and characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, Fourier transform infrared (FTIR) spectroscopy, and UV/vis spectroscopy to examine the morphology, composition, and functional groups of the photocatalyst. Parameters including pH, dosage, dye concentration, scavengers, and effects of oxidizing agents were considered. Under optimal conditions, the degradations were 95.7 and 88.9% for RBV-5R and FY AB, respectively, in 60 min. The pH and oxidizing agents played important roles in the degradation process. Only 43.8 and 32.5% of RBV-5R and FY AB, respectively, were degraded in the absence of an oxidizing agent. With the addition of oxidizing agents, 95.7 and 88.9% of RBV-5R and FY AB degradation occurred, respectively. The optimal pH values for RBV 5-R and FY-AB were 8 and 12, respectively. A comparison between the photocatalytic and sonophotocatalytic processes revealed degradation efficiencies of 41 and 33% for RBV-5R and FY-AB, respectively, by the photocatalytic process. Therefore, results indicate the productivity of the sonophotocatalytic degradation process.

Significantly Enhanced Electrocatalytic Reduction of Chloramphenicol from Water Mediated by Fe–F–N Co-doped Carbon Materials

Chloramphenicol (CAP) is a widely used antibiotic drug and poses a great threat to human health and the ecosystem. In this work, an iron–fluorine–nitrogen (Fe–F–N) co-doped porous carbon material was innovatively prepared and applied for the electrocatalytic reduction of CAP from water, and excellent treatment performance was achieved. For an initial CAP concentration of 10 mg/L, after 60 min operation, almost 100% of CAP was removed. The active Fe(II) sites and the F-doping-induced electronic structure of Fe-FNC facilitated the electrocatalytic reductive degradation of CAP by promoting electron transfer, rather than the H*-mediated indirect reduction process. Therefore, a better treatment performance was obtained by Fe-FNC compared to other catalysts such as Fe-NC and FNC. The reaction pathways for CAP reduction were elucidated, and the ecotoxicity of the reaction products was assessed. The toxicity of the intermediate products was found to be significantly reduced, indicative of the good prospect of this method for CAP-containing wastewater pretreatment.

Fine Recycled Concrete Aggregates Treated by Means of Wastewater and Carbonation Pretreatment

Fine recycled concrete aggregate (FRCA) possesses substantial limitations for its use due to its significant porosity. Extensive research on the effect of carbonation on the accessible porosity of coarse recycled concrete aggregate is available in the literature, but FRCA information is scarce. The present paper presents results of the effect of carbonation on different fractions of FRCA from <0.125 mm to 4 mm previously sprayed with wastewater from mortar production as an additional source of portlandite. The results of water absorption via the electrical conductivity method, TGA, XRD+Rietveld+PONKCS analysis, EDS mapping, and Life Cycle Assessment (LCA) demonstrate that the efficiency of the treatment depends on the particle size range of the FRCA. It was most effective for the extreme size fractions <0.25 mm and >1 mm of FRCA as a result of the relationship between the amount of precipitated calcium carbonate and the initially accessible porosity in each fraction. As a consequence, mortar produced with 30% replacement of natural sand with carbonated FRCA showed no impact on compressive strength.

A comparison study of heat-assisted Fe2+/persulfate and powdered activated carbon/persulfate wastewater pre-treatment for membrane fouling alleviation

Heat/Fe2+/persulfate (PS) and heat/powdered activated carbon (PAC)/PS exhibit oxidation, coagulation, and adsorption effects, respectively. However, no studies have been conducted to discuss and compare the synergistic contribution to membrane fouling mitigation under thermal synergy. Herein, heat/Fe2+/PS and heat/PAC/PS systems were used to alleviate membrane fouling during municipal wastewater recycling in an aerobic granular sludge membrane bioreactor (AGMBR), and the effects of oxidation, coagulation, and adsorption on the membrane fouling mitigation were analyzed. The results showed that heat/Fe2+/PS and heat/PAC/PS effectively increased the filtration flux, decreased the fouling resistance, and maintained the membrane surface morphology. Compared to heat/PAC/PS, the heat/Fe2+/PS exhibited better control of membrane fouling owing to the generation of sulfate radicals and Fe3+. The non-radical effect is an important way to mitigate membrane fouling by heat/PAC/PS. Moreover, the pretreatment systems were effective in decomposition and removal of large-particle-size pollutants owing to their excellent oxidation capacity. According to the extended Derjaguin–Landau–Verwey–Overbeek theory, the heat/Fe2+/PS system had the higher energy barrier values of foulant–membrane (155.31 kT) and foulant–foulant (113.75 kT). The cake filtration and intermediate blocking models were the major mechanisms of membrane fouling, and efficient removal of chemical oxygen demand (R2>0.93) and suspended solids (R2>0.92) were beneficial to the membrane fouling mitigation. This study elucidates the differences in the mechanisms of heat/Fe2+/PS and heat/PAC/PS in mitigating AGMBR membrane fouling.

Source preventing mechanism of florfenicol resistance risk in water by VUV/UV/sulfite advanced reduction pretreatment

To avoid the inhibition of microbial activity and the emergence of bacterial resistance, effective abiotic pretreatment methods to eliminate the antibacterial activity of target antibiotics before the biotreatment system for antibiotic-containing wastewater are necessary. In this study, the VUV/UV/sulfite system was developed as a pretreatment technique for the source elimination of florfenicol (FLO) resistance risk. Compared with the VUV/UV/persulfate and sole VUV photolysis, the VUV/UV/sulfite system had the highest decomposition rate (0.33 min‒1) and the highest defluorination (83.0%), resulting in the efficient elimination of FLO antibacterial activity with less than 2.0% mineralization, which would effectively retain the carbon sources for the sludge microorganisms in the subsequent biotreatment process. Furthermore, H• was confirmed to play a more important role in the elimination of FLO antibacterial activity by controlling the environmental conditions for the formation and transformation of reactive species and adding their scavengers. Based on the theoretical calculation and proposed photolytic intermediates, the elimination of FLO antibacterial activity was achieved by dechlorination, defluorination and removal of sulfomethyl groups. When the pretreated FLO-containing wastewater entered the biological treatment unit, the abundance of associated antibiotic resistance genes (ARGs) and the relative abundance of integrons were efficiently prevented by approximately 55.4% and 22.9%, respectively. These results demonstrated that the VUV/UV/sulfite system could be adopted as a promising pretreatment option for the source elimination of FLO resistance risk by target decomposition of its responsible structures before the subsequent biotreatment process.

Circular Economy Approach in Treatment of Galvanic Wastewater Employing Membrane Processes

According to the idea of sustainable development, humanity should make every effort to care for the natural environment along with economic development. Decreasing water resources in the world makes it necessary to take action to reduce the consumption of this resource. This article presents the results of research conducted to improve the use of recyclable materials in line with the circular economy model. The research focused on the development of a technological solution for the recovery of raw materials from galvanic wastewater. The concept of a galvanic wastewater treatment system presented in the article includes wastewater pre-treatment in the ultrafiltration (UF) process and water recovery in the reverse osmosis (RO) process. In addition, the purpose of the work was to manage post-filtration waste (RO retentate) containing high concentrations of zinc in the process of galvanizing metal details. The obtained results indicate that it is possible to reduce the amount of sewage from the galvanizing industry by reusing the recovered water as technical water in the process line. The carried-out model tests of galvanizing confirmed the possibility of using RO retentate for the production of metal parts. The achieved results are a proposal to solve the problem of reducing the impact of galvanic wastewater on the environment and to improve the profitability of existing galvanizing technologies by reducing the consumption of water and raw materials.

Performance and cost-benefit analysis of anaerobic moving bed biofilm reactor for pretreatment of textile wastewater.

Performance of an anaerobic moving bed biofilm reactor (AnMBBR) was evaluated for pretreatment of real textile desizing wastewater at organic loading rate (OLR) of 1±0.05 to 6.3±0.37 kgCOD/m3/d. After OLR optimization, the performance of AnMBBR was evaluated for biodegradation of reactive dyes. AnMBBR was operated under a mesophilic temperature range of 30 to 36 °C, while the oxidation-reduction potential (ORP) and pH were in the range of 504 to 594 (-mV) and 6.98 to 7.28, respectively. By increasing the OLR from 1±0.05 to 6.3±0.37 kgCOD/m3/d, COD and BOD5 removal was decreased from 84 to 39% and 89 to 49%, respectively. While the production of biogas was increased from 0.12 to 0.83 L/L·d up to an optimum OLR of 4.9±0.43 kgCOD/m3/d. With increase in the dye concentration in the feed, COD, BOD5, color removal and biogas production reduced from 56, 63, 70% and 0.65 L/L·d to 34, 43, 41% and 0.08 L/L·d, respectively. Based on the data obtained, a cost-benefit analysis of AnMBBR was also investigated for the pretreatment of real textile desizing wastewater. Cost estimation of anaerobic pretreatment of textile desizing wastewater indicated a net profit of 21.09 million PKR/yr (114,000 €/yr) and a potential payback period of 2.54 years.

Effects of wastewater pre-treatment on clogging of an intermittent sand filter

Intermittent sand filters (ISFs) are widely used in rural areas to treat domestic and dilute agricultural wastewater due to their simplicity, efficacy and relative low cost. However, filter clogging reduces their operational lifetime and sustainability. To reduce the potential of filter clogging, this study examined pre-treatment of dairy wastewater (DWW) by coagulation with ferric chloride (FeCl3) prior to treatment in replicated, pilot-scale ISFs. Over the study duration and at the end of the study, the extent of clogging across hybrid coagulation-ISFs was quantified, and the results were compared to ISFs treating raw DWW without a coagulation pre-treatment, but otherwise operated under the same conditions. During operation, ISFs receiving raw DWW recorded higher volumetric moisture content (θv) than ISFs treating pre-treated DWW, which indicated that biomass growth and clogging rate was higher in ISFs treating raw DWW, which were fully clogged after 280 days of operation. The hybrid coagulation-ISFs remained fully operational until the end of the study. Examination of the field-saturated hydraulic conductivity (Kfs) showed that ISFs treating raw DWW lost approximately 85 % of their infiltration capacity in the uppermost layer due to biomass build-up versus 40 % loss for hybrid coagulation-ISFs. Furthermore, loss on ignition (LOI) results indicated that conventional ISFs developed five times the organic matter (OM) in the uppermost layer compared to ISFs treating pre-treated DWW. Similar trends were observed for phosphorus, nitrogen and sulphur, where proportionally higher values were observed for raw DWW ISFs than pre-treated DWW ISFs, with values decreasing with depth. Scanning electron microscopy (SEM) showed a clogging biofilm layer on the surface of raw DWW ISFs, while pre-treated ISFs maintained distinguishable sand grains on the surface. Overall, hybrid coagulation-ISFs are likely to sustain infiltration capacity for a longer period than filters treating raw wastewater; therefore, requiring smaller surface area for treatment and minimal maintenance.

Integrated sonophotocatalytic oxidation and SBR processes for the effective treatment of antibiotics with an emphasis on process optimization and microbial diversity

The presence of antibiotics in water and wastewater is a serious environmental concern of emerging interest globally. Their effective removal with a single treatment process is, however, challenging because of their widely varying characteristics, and requires innovative integration of treatment processes. In this study, sonophotocatalytic oxidation process was integrated with an aerobic sequencing batch reactor (SBR) for the comprehensive removal of a mixture of antibiotics. Initially, a Central Composite Design using Response Surface Methodology was used to optimise the operational parameters, viz. ultrasound (US) frequency, pH, and catalyst dosage, for the removal of Ciprofloxacin (CPX), Amoxicillin (AMX), and Tetracycline (TTC) in simulated wastewater. An optimised condition of 20 kHz US frequency, 6.59 initial pH, and 0.94 g L−1 catalyst dosage was observed for the maximum pollutant removal. These experimental conditions were subsequently used for combined sonophotocatalysis-aerobic SBR treatment. Three SBR systems representing a control system, pre-treated system, and untreated system, were used for the study. All three systems were able to achieve an average COD and NH4+-N removal of 85 % and 98 %, respectively. Results from the biological systems concluded that an enhanced CPX and TTC removal was observed in the pre-treated system, whereas maximum AMX removal was observed in the untreated SBR system. The metagenomic analysis confirmed the significant difference of microbial species with the addition of pretreated and untreated wastewater into the biological reactor, and pretreated system having higher number of species and greater biodiversity in comparison to untreated system.

Recovery of nickel from actual electroplating wastewater by integrated electrodeposition with adsorption pretreatment technique

The rapidly growing electroplating industry has led to the discharge of large amounts of wastewater containing heavy metals. Electrodeposition technique can recover metals from wastewater, however, its application involves high energy costs due to the high levels of inorganic and organic impurities, including metal ions, that are usually present in real effluents. Therefore, in the present work, integrated electrodeposition with adsorption pretreatment technique was employed to recover nickel from real electroplating wastewater in a cost-effective manner. The results showed that adsorption pretreatment technique could simplify the nature of the wastewater by removing 85% of TOC from real electroplating wastewater. Further, the pretreated wastewater was used for electrodeposition and the results indicated that the electrodeposition could reduce the ineffective energy consumption by 50% (from 44 kw∙h/kg to 35 kw∙h/kg) for actual wastewater, compared to the effective energy consumption of 28 kw∙h/kg for simulated wastewater which hinted that the pretreatment by adsorption technique had a positive effect on the deposition of nickel. Analysis of the deposits showed that the recovered nickel was mainly in the form of zero-valent nickel or oxides. The zero-valent nickel adhered tightly to the electrode plates, while the oxide form mainly adhered to the electrode plates or fell off into the electrolyte. Importantly, the findings of EDS and XRD showed that both simulated and actual wastewater yielded high-purity metallic nickel. Overall, this work provided an effective way to promote the application of integrated electrodeposition with adsorption pretreatment technique for the recovery of precious metals from real electroplating wastewater.

Mainstream wastewater treatment by polyaluminium ferric chloride (PAFC) flocculation and nitritation-denitritation membrane aerated biofilm reactor (MABR)

To reduce the carbon emission of sewage treatment, a novel adsorption-biodegradation (A-B) process, flocculation pretreatment as A-stage and nitritation-denitritation MABR as B-stage, was proposed in the study. It was found that 27.37 %–49.69 % of organics can be removed from actual wastewater by flocculation with polyaluminium ferric chloride (PAFC). The pretreated wastewater could be further treated by nitritation-denitritation MABR with low aeration pressure (2–5 kPa) without any extra organics. The NH4+-N, total nitrogen (TN), and chemical oxygen demand (COD) removal efficiency can reach 100 %, 84.04 %, and 98.54 %, respectively. It was also found that the relative abundances of ammonia-oxidizing bacteria (AOB) (3.81 %–4.76 %) and denitrifying bacteria (DB) (4.30 %–5.59 %) were higher than that of nitrite-oxidizing bacteria (NOB) (2.08 %–2.39 %) in the MABR even after 130 days of operation according to the microorganism identification by 16S rRNA sequencing technology. This implied that low oxygen aeration in MABR can prevent NOB from becoming dominant bacteria. Furthermore, it was found that there were indeed traces of anaerobic ammonia oxidation (Anammox) bacteria (0.04 %–0.08 %) and were closely surrounded by other microorganisms in the MABR based on fluorescence in situ hybridization (FISH) technology. In addition, the microbial nitrogen metabolism process in the MABR was further analyzed according to the Kyoto Encyclopedia of Genes and Genomes (KEGG). The promising mainstream A-B process proposed in this study was expected to achieve nitrogen removal with little carbon and energy consumption in wastewater treatment plants (WWTPs).

Pretreatment of septic tank wastewater by packed anaerobic baffled reactor: Pollutant degradation and microbial community succession in different compartments

Anaerobic baffled reactor (ABR) is widely used in rural sewage treatment due to its unique structure, strong impact load resistance, and low energy consumption. However, there is a lack of research on pollutant degradation patterns and microbial community succession patterns in each compartment of ABR. In this study, a packed anaerobic baffled reactor (PABR) was constructed. The effects of T and HRT on the pollutant removal performance of PABR were investigated, and the pollutant degradation and microbial community succession in different compartments of PABR were studied. The results show that the removal rates of COD, NH4+-N, and TN of PABR can reach 85.54 ± 1.08%, 16.94 ± 1.01%, and 5.64 ± 1.18% respectively, and PABR has a good pollutant removal effect. With the extension of HRT, the COD removal rate of PABR increases steadily, and the NH4+-N and TN removal rate of PABR increases to a certain extent. The recommended HRT is 72 h. T has a significant impact on the COD removal effect of PABR. The increase of T in a certain range is conducive to the removal of pollutants by PABR. The COD removal rate of PABR decreases gradually along the flow direction, and the removal of organic matter is mainly concentrated in the first compartment. PABR has good removal capacity for CODss and better nitrogen removal capacity compared with traditional ABR. The richness and diversity of the microbial community in PABR increased gradually along the flow direction. The bacterial species in each compartment were similar but the proportion was different, showing the characteristics of multi-stage and separated phase operation. This study provides a new reference for the application of ABR in rural sewage treatment.

Pretreatment of Biogas Slurry by Modified Biochars to Promote High-Value Treatment of Wastewater by Microalgae

High concentrations of contaminants such as ammonia nitrogen and organic matter in full-strength wastewater severely inhibit the growth of microalgae, contributing to lower biomass accumulation and contaminant removal efficiency. To overcome this limitation, modified biochars prepared from pine sawdust and sugarcane bagasse were used in this study as an adsorbent–desorbent for the pretreatment of wastewater to promote the growth of microalgae. The results showed that the two modification methods (acid/alkaline modification and magnesium salt modification) used in the experiment could increase the abundance of oxygen-containing functional groups. Moreover, magnesium salt modification could effectively improve the pore structure of biochar surfaces and increase the specific surface areas. Compared with the pristine biochars, the adsorption performance of the modified biochar was found to be significantly higher for nutrients in wastewater. The adsorption capacity of the acid/alkaline-modified pine sawdust biochar reached 8.5 and 16.49 mg∙g−1 for ammonia nitrogen and total organic carbon in wastewater, respectively. The magnesium salt modified pine sawdust biochar achieved a more comprehensive nutrients adsorption capacity of 15.68, 14.39, and 3.68 mg∙L−1 for ammonia nitrogen, total organic carbon, and total phosphorus, respectively. The mechanism of ammonia nitrogen adsorption was mainly the complexation of surface -OH functional groups, while the adsorption mechanism for phosphate was mainly the complexation of -OH and Mg-O functional groups and the chemical precipitation of MgO or Mg(OH)2 attached to the surface.

Characteristic analysis of s-Fe/Cu two-component micro-electrolysis materials and degradation of dye wastewater.

Micro-electrolysis is a pretreatment technology for difficult-to-biodegrade wastewater. In this study, a chemical displacement method was used to load copper on the surface of sponge iron (s-Fe), and then it was mixed with activated carbon and other components to obtain a multi-element micro-electrolytic filler (OMEF). Through BET, SEM, XRD, XPS, and FT-IR characterization and analysis, OMEF was proved to have a specific surface area of 88.374 m2/g, C-C, C-O, C = O, O-C = O, and other functional groups and Fe3C, MnO2 and other active materials. The removal mechanism of organic pollutants in wastewater by OMEF could be due to the galvanic reaction, direct reduction of Fe, oxidation of Fe, catalytic oxidation of Cu and Mn, and co-precipitation of adsorption. The coupling of the micro-electrolysis and biological methods proved that OMEF had excellent application efficiency. The results indicated that the COD removal rates of OMEF and commercial fillers reached 88.39% and 48.02%, respectively, and the B/C reached 0.74 and 0.3. OMEF showed a better performance. The reusability of the OMEF filler was measured to ensure that the B/C was maintained at around 0.5 during 5 cycles. Kinetic analysis showed that the degradation data of methyl orange (MO) and the removal data of COD obeyed pseudo-second-order kinetics. Moreover, it can further broaden the pH range of treated wastewater and increase the oxidation rate. This new strategy has brought potential enlightenment for the development of high-efficiency wastewater pretreatment using new micro-electrolysis materials. The excellent performance of OMEF micro-electrolytic filler in pretreatment indicated its potential for industrial application.

Extraction of polyhydroxyalkanoate from activated sludge using supercritical carbon dioxide process and biopolymer characterization

Polyhydroxyalkanoates (PHA) are biodegradable polymers and have the potential to substitute with fossil-fuel based polymers since they have similar properties. Many studies on the production of PHA have been conducted, but the extraction/purification processes have received less attention. Mostly, solvent extraction has been studied, and the effect of different solvent types on the separation processes have been investigated. A better extraction method for PHA makes it a feasible alternative to fossil-fuel based polymers. In this study, a new protocol for the extraction of PHA from activated sludge by supercritical carbon dioxide disruption (sCO2) and biopolymer recovery from disrupted cells were proposed. Extraction experiments were carried out with sCO2 at different pressures, temperatures, times, biomass amounts, and modifier volumes. The operation yield was expressed based on the polyhydroxybutyrate (PHB) release efficiency. The biomass for the extraction experiments was obtained from a PHA production reactor where activated sludge was fed with anaerobically pretreated yeast industry wastewater. 80 % PHB releasing efficiency was achieved by disturbing 2 g of biomass at a density of 57 g/L (biomass/volume) with sCO2 at 200 bar pressure for 15 min at 40 °C. The PHB purity and molecular weight (Mv) of biopolymers were 80 % and 0.27•106 respectively. The use of methanol as a modifier during the sCO2 disruption increased the Mv to 0.37•106. Characterization studies by Fourier transform infrared spectroscopy (FTIR) and thermal degradation analysis (TGA) demonstrated that the biopolymer recovered with this extraction protocol was comparable to commercial PHB. As a clear advantage over the other extraction protocols; operationally fast and simple extraction procedure was achieved.

Electrostimulation triggers an increase in cross-niche microbial associations toward enhancing organic nitrogen wastewater treatment

As an efficient wastewater pretreatment biotechnology, electrostimulated hydrolysis acidification (eHA) has been used to accelerate the removal of refractory pollutants, which is closely related to the effects of electrostimulation on microbial interspecies associations. However, the ecological processes underpinning such linkages remain unresolved, especially for the microbial communities derived from different niches, such as the electrode surface and plankton. Herein, the principles of cross-niche microbial associations and community assembly were investigated using molecular ecological network and phylogenetic bin-based null model analysis (iCAMP) based on 16S rRNA gene sequences. The electrostimulated planktonic sludge and electrode biofilm displayed significantly (P < 0.05) 1.67 and 1.53 times higher organic nitrogen pollutant (azo dye Alizarin Yellow R) degradation efficiency than non-electrostimulation group, and the corresponding microbial community composition and structure were significantly (P < 0.05) changed. Electroactive bacteria and functional degraders were enriched in the electrode biofilm and planktonic sludge, respectively. Notably, electrostimulation strengthened the synergistic microbial associations (1.8 times more links) between sludge and biofilm members. Additionally, both electrostimulation and cross-niche microbial associations induced greater importance of deterministic assembly. Overall, this study highlights the specificity of cross-electrode surface microbial associations and ecological processes with electrostimulation and advances our understanding of the manipulation of sludge microbiomes in engineered wastewater treatment systems.

Photocatalytic pretreatment of dairy wastewater and benefits of the photocatalyst as an enhancer of anaerobic digestion

High-fat wastes are difficult to degrade and mineralize under biological methods. It is imperative to identify suitable combinations of physicochemical and biological processes. This study analyzed the prospects of combining photocatalysis and anaerobic digestion of dairy wastewater using a nano-catalyst made of reduced graphene oxide (RGO) and nano-zerovalent iron (NZVI). The operational parameters of ammonium persulfate (APS) assisted photocatalytic pretreatment, initial pH (4–9), organic loading (2200–17,900 mg L−1) and catalyst dosage (0.1–0.5 g) were optimized. The maximum solubilization was found at an initial pH 5 until 4 h of pretreatment with an increase of 38.77 ± 0.85 % soluble chemical oxygen demand (SCOD) and 39.05 ± 1.3 % dissolved organic carbon (DOC). The anaerobic digestion of pretreated wastewater containing spent catalyst was carried out with slight amendment of fresh catalyst (D1) and without any fresh supplement (D2). The total biogas produced in D1 and D2 in 28 days was 31.69 ± 1.05 % and 7.14 ± 0.15 % more than that obtained from the control digester (CD) respectively. Also, D1 and D2 exhibited better CH4 production, which was 81.01 ± 3.24 % and 38.93 ± 1.1 % more than CD. D1 exhibited better removal of SCOD with 72.99 ± 2.84 % efficiency, whereas, D2 and CD showed only 67.72 ± 2.91 % and 61.08 ± 1.89 % respectively. According to the modified Gompertz model, the lag phase time (λ) for CD is more than D1 and D2.

Application Potential of Constructed Wetlands on Different Operation Mode for Biologically Pre-Treatment of Rural Domestic Wastewater

In order to satisfy the requirements of rural domestic sewage, a bio-ecological combination system was proposed, including a biological treatment section (anaerobic hydrolysis tank and aerobic tank) and an ecological post-treatment section. This study observed the application potential of constructed wetlands (CW) on different operation modes for biologically pre-treated rural domestic wastewater. The organics and nutrient removal efficiency of the tidal flow constructed wetland (TFCW) and the horizontal subsurface flow constructed wetland (HFCW) were compared at a temperature range of 20–40 °C. During the stable phase, the higher chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and total phosphorus (TP) removal efficiencies existed in TFCW than HFCW, corresponding to the efficiency of COD 69.46%, NH4+-N 96.47%, and TP 57.38%, but lower performance on COD (61.43%), NH4+-N (84.99%), and TP (46.75%) removal in HFCW, which should be attributed to the increasement of aerobic heterotrophic bacteria (Arthrobact and Sphingomonas), nitrifiers (Nitrospira), and phosphate accumulating organisms (PAOs) (Pseudomonas). The microbial biomass was also increased from 2.13 ± 0.14 mg/g (HFCW) to 4.64 ± 0.18 mg/g (TFCW), which proved to strengthen the formation and growth of biofilm under a better oxygen supplement. Based on the relative abundance of functional genera in the microbial community, it showed that TFCW was more favorable for promoting the growth of heterotrophic bacteria, nitrifiers, and phosphate-accumulating organisms (PAOs). When temperature changed from −4 °C to 15 °C, the two-stage constructed wetlands (TFCW-HFCW and HFCW-TFCW) were used for improving the performance of pollutants removal. The results demonstrated that the effluent concentrations of TFCW-HFCW and HFCW-TFCW met the Class 1A discharge standard of DB32/3462-2020 in JiangSu Province, China. Therefore, this study will provide a useful and easy-to-implement technology for the operation as an ecological post-treatment section.