There is a pressing need for efficient biological treatment systems for the removal of organic compounds in greywater given the rapid increase in household wastewater produced as a consequence of rapid urbanisation. Moreover, proper treatment of greywater allows its reuse that can significantly reduce the demand for freshwater supplies. Herein, we demonstrate the possibility of enhancing the removal efficiency of solid contaminants from greywater using MHz-order surface acoustic waves (SAWs). A key distinction of the use of these high frequency surface acoustic waves, compared to previous work on its lower frequency (kHz order) bulk ultrasound counterpart for wastewater treatment, is the absence of cavitation, which can inflict considerable damage on bacteria, thus limiting the intensity and duration, and hence the efficiency enhancement, associated with the acoustic exposure. In particular, we show that up to fivefold improvement in the removal efficiency can be obtained, primarily due to the ability of the acoustic pressure field in homogenizing and reducing the size of bacterial clusters in the sample, therefore providing a larger surface area that promotes greater bacteria digestion. Alternatively, the SAW exposure allows the reduction in the treatment duration to achieve a given level of removal efficiency, thus facilitating higher treatment rates and hence processing throughput. Given the low-cost of the miniature chipscale platform, these promising results highlight its possibility for portable greywater treatment for domestic use or for large-scale industrial wastewater processing through massive parallelization.
The increasing number and concentration of organic pollutants in water stream could become a serious threat in the near future. Magnetite has the potential to degrade pollutants via photocatalysis with a convenient separation process. This study discusses in detail the control size and morphology of magnetite nanoparticles, and their composites with co-precipitation, hydrothermal, sol-gel, and electrochemical route. Further photocatalytic enhancement with the addition of metal and porous support was proposed. This paper also discussed the technology to extend the lifetime of recombination through an in-depth explanation of charge transfer. The possibility to use waste materials as catalyst support was also elucidated. However, magnetite-based photocatalysts still require many improvements to meet commercialization criteria.
Many developing countries, mostly situated in the tropical region, have incorporated a biological nitrogen removal process into their wastewater treatment plants (WWTPs). Existing wastewater characteristic data suggested that the soluble chemical oxygen demand (COD) in tropical wastewater is not sufficient for denitrification. Warm wastewater temperature (30 °C) in the tropical region may accelerate the hydrolysis of particulate settleable solids (PSS) to provide slowly-biodegradable COD (sbCOD) for denitrification. This study aimed to characterize the different fractions of COD in several sources of low COD-to-nitrogen (COD/N) tropical wastewater. We characterized the wastewater samples from six WWTPs in Malaysia for 22 months. We determined the fractions of COD in the wastewater by nitrate uptake rate experiments. The PSS hydrolysis kinetic coefficients were determined at tropical temperature using an oxygen uptake rate experiment. The wastewater samples were low in readily-biodegradable COD (rbCOD), which made up 3-40% of total COD (TCOD). Most of the biodegradable organics were in the form of sbCOD (15-60% of TCOD), which was sufficient for complete denitrification. The PSS hydrolysis rate was two times higher than that at 20 °C. The high PSS hydrolysis rate may provide sufficient sbCOD to achieve effective biological nitrogen removal at WWTPs in the tropical region.
Biogranulation is an effective biological technology suitable for the treatment of various wastewaters. However, the major drawback of this technique is the long start-up period for biogranule development. Hence, the primary focus of this study was on cell surface hydrophobicity which is the main parameter that indicates cell agglomeration during the initial self-immobilization process of aerobic granulation. The effects of sludge concentration and magnetic activated carbon on cell surface hydrophobicity were investigated in this study. Response surface methodology (RSM) was applied to design, analyze, and optimize the outcome of the study. Experiments were performed at sludge concentration of 1,000-3,000 mg/L and magnetic activated carbon mass of 1-5 g/L with 24 hr of aeration time. The results show that both variables yielded a positive significant effect on the initial development of aerobic granulation with 56% surface hydrophobicity. Interaction effects between variables on the responses were significant with positive estimated interaction effect at all different measured aeration time. The magnetic activated carbon acted as nuclei to induce bacterial attachment and further enhanced the initial process of biogranule development under optimal condition of 1:1.1 (sludge concentration: magnetic activated carbon). PRACTITIONER POINTS: Cell surface hydrophobicity was evaluated Magnetic activated carbon enhanced cell surface hydrophobicity Response surface methodology was employed for analyses Magnetic activate carbon mass and biomass concentration was significant Magnetic activated carbon acted as nuclei to improve biogranulation.
This review investigates the performance and the feasibility of the integration of an algal reactor in recirculating aquaculture systems (RAS). The number of studies related to this topic is limited, despite the apparent benefit of algae that can assimilate part of the inorganic waste in RAS. We identified two major challenges related to algal integration in RAS: first, the practical feasibility for improving nitrogen removal performance by algae in RAS; second, the economic feasibility of integrating an algal reactor in RAS. The main factors that determine high algal nitrogen removal rates are light and hydraulic retention time (HRT). Besides these factors, nitrogen-loading rates and RAS configuration could be important to ensure algal performance in nitrogen removal. Since nitrogen removal rate by algae is determined by HRT, this will affect the size (area or volume) of the algal reactor due to the time required for nutrient uptake by algae and large surface area needed to capture enough light. Constraints related to design, space, light capture, and reactor management could incur additional cost for aquaculture production. However, the increased purification of RAS wastewater could reduce the cost of water discharge in places where this is subject to levees. We believe that an improved understanding of how to manage the algal reactor and technological advancement of culturing algae, such as improved algal reactor design and low-cost artificial light, will increase the practical and economic feasibility of algal integration in RAS, thus improving the potential of mass cultivation of algae in RAS.
Cattle slaughterhouses generate wastewater that is rich in organic contaminant and nutrients, which is considered as high strength wastewater with a high potential for energy recovery. Work was undertaken to evaluate the efficiency of the 12 L laboratory scale conventional and a modified upflow anaerobic sludge blanket (UASB) reactors (conventional, R1 and modified, R2), for treatment of cattle slaughterhouse wastewater (CSWW) under mesophilic condition (35 ± 1 °C). Both reactors were acclimated with synthetic wastewater for 30 days, then continuous study with real CSWW proceeds. The reactors were subjected to the same loading condition of OLR, starting from 1.75, 3, 5 10, 14, and 16 g L-1d-1, corresponding to 3.5, 6, 10, 20, 28, and 32 g COD/L at constant hydraulic retention time (HRT) of 24 h. The performance of the R1 reactor drastically dropped at OLR 10 g L-1d-1, and this significantly affected the subsequent stages. The steady-state performance of the R2 reactor under the same loading condition as the R1 reactor revealed a high COD removal efficiency of 94% and biogas and methane productions were 27 L/d and 89%. The SMP was 0.21 LCH4/gCOD added, whereas the NH3-N alkalinity ratio stood at 651 mg/L and 0.2. SEM showed that the R2 reactor was dominated by Methanosarcina bacterial species, while the R1 reactor revealed a disturb sludge with insufficient microbial biomass.
The petrochemical wastewater (PCW) from acrylic acid plants possesses a very high chemical oxygen demand (COD) due to the presence of acrylic acid along with other organic acids. The treatment of PCW by conventional aerobic and anaerobic methods is energy intensive. Therefore, the treatment of PCW with concurrent power generation by employing microbial fuel cell (MFC) could be a potential alternative to solve the energy and environmental issues. This study demonstrates the potentiality of PCW from acrylic acid plant with an initial COD of 45,000 mg L-1 generating maximum power density of 850 mW m-2 at a current density of 1500 mA m-2 using acclimatized anaerobic sludge (AS) as biocatalyst. The predominant microbes present in acclimatized AS were identified using Biolog GEN III analysis, which include the electrogenic genera namely Pseudomonas spp. and Bacillus spp. along with methanogenic archea Methanobacterium spp. The mechanism of electron transfer was elucidated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) which clearly demonstrated the natural metabolite-based electron transfer across the electrode/biofilm/solution interface. The abundance of the electron shuttle metabolites was increased with the microbial growth in the bulk solution as well as in the biofilm leading to a high power generation. The COD removal efficiency and the coulombic efficiency (CE) were found to be 40% and 21%, respectively after 11 days of operation using initial COD of 45,000 mg L-1. The low COD removal efficiency could drastically be increased to 82% when the initial COD of PCW was 5000 mg L-1 generating a power density of 150 mW m-2. The current work proves the feasibility of the MFC for the treatment of acrylic acid plant PCW using acclimatized anaerobic sludge (AS) as a biocatalyst.
A moderately halophilic bacterium isolated from fermenting shrimp paste, Salinivibrio sp. M318 was found capable of using fish sauce and mixtures of waste fish oil and glycerol as nitrogen and carbon sources, respectively, for poly(3-hydroxybutyrate) (PHB) production. A cell dry weight (CDW) of up to 10 g/L and PHB content of 51.7 wt% were obtained after 48 h of cultivation in flask experiment. Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] was synthesized when 1,4-butanediol, γ-butyrolactone, or sodium 4-hydroxybutyrate was added as precursors to the culture medium. The biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] was achieved by supplying precursors such as sodium valerate, sodium propionate, and sodium heptanoate. Salinivibrio sp. M318 was able to accumulate the above mentioned PHAs during the growth phase. High CDW of 69.1 g/L and PHB content of 51.5 wt% were obtained by strain Salinivibrio sp. M318 after 78 h of cultivation in fed-batch culture. The results demonstrate Salinivibrio sp. M318 to be a promising wild-type bacterium for the production of PHA from aquaculture residues.
The pollution of water resources due to the disposal of industrial wastes that have organic material like phenol is causing worldwide concern because of their toxicity towards aquatic life, human beings and the environment. Phenol causes nervous system damage, renal kidney disease, mental retardation, cancer and anaemia. In this study, magnetic palm kernel biochar is used for removal of phenol from wastewater. The effect of parameters such as pH, agitation speed, contact time and magnetic biochar dosage are validated using design of experiments. The statistical analysis reveals that the optimum conditions for the highest removal (93.39%) of phenol are obtained at pH of 8, magnetic biochar dosage of 0.6 g, agitation speed at 180 rpm and time of 60 min with the initial concentration of 10 mg/L. The maximum adsorption capacities of phenol were found to be 10.84 mg/g and Langmuir and Freundlich isotherm models match the experimental data very well and adsorption kinetic obeys a pseudo-second order. Hence, magnetic palm kernel can be a potential candidate for phenol removal from wastewater.
Many wastewater treatment plants (WWTPs) operating in biological nitrogen removal activated sludge process in the tropics are facing the pressure of increasingly stringent effluent standards while seeking solutions to reduce the plants' energy consumption and operating cost. This study investigated the feasibility of applying low-dissolved oxygen (low-DO) nitrification and utilizing slowly-biodegradable chemical oxygen demand (sbCOD) for denitrification, which helps to reduce energy usage and operating cost in treating low soluble COD-to-nitrogen tropical wastewater. The tropical wastewater was first characterized using wastewater fractionation and respirometry batch tests. Then, a lab-scale sequencing batch reactor (SBR) was operated to evaluate the long-term stability of low-DO nitrification and utilizing sbCOD for denitrification in an anoxic-oxic (AO) process treating tropical wastewater. The wastewater fractionation experiment revealed that particulate settleable solids (PSS) in the wastewater provided slowly-biodegradable COD (sbCOD), which made up the major part (51 ± 10%) of the total COD. The PSS hydrolysis rate constant at tropical temperature (30 °C) was 2.5 times higher than that at 20 °C, suggesting that sbCOD may be utilized for denitrification. During the SBR operation, high nitrification efficiency (93 ± 6%) was attained at low-DO condition (0.9 ± 0.1 mg O2/L). Utilizing sbCOD for post-anoxic denitrification in the SBR reduced the effluent nitrate concentration. Quantitative polymerase chain reaction, 16S rRNA amplicon sequencing and fluorescence in-situ hybridization revealed that the genus Nitrospira was a dominant nitrifier. 16S rRNA amplicon sequencing result suggested that 50% of the Nitrospira-related operational taxonomic units were affiliated with comammox, which may imply that the low-DO condition and the warm wastewater promoted their growth. The nitrogen removal in a tropical AO process was enhanced by incorporating low-DO nitrification and utilizing sbCOD for post-anoxic denitrification, which contributes to an improved energy sustainability of WWTPs.
In this work, synergistic effect of solar photocatalysis integrated with adsorption process towards the degradation of Congo red (CR) was investigated via two different approaches using a photocatalytic membrane reactor. In the first approach, sequential treatments were conducted through the adsorption by graphene oxide (GO) and then followed by photocatalytic oxidation using Fe-doped ZnO nanocomposites (NCs). In the second approach, however, CR solution was treated by photocatalytic oxidation using Fe-doped ZnO/rGO NCs. These nanocomposites were synthesized by a sol-gel method. The NCs were characterized by X-ray diffraction (XRD), photoluminescence (PL), Fourier transmission infrared (FTIR), ultraviolet-visible (UV-vis) spectroscopy, and field emission scanning electron microscopy (FESEM). It was observed that Fe-doped ZnO could enhance the photoactivity of ZnO under solar light. When Fe-doped ZnO were decorated on GO sheets, however, this provided a surface enhancement for adsorption of organic pollutants. The photocatalytic performances using both approaches were evaluated based on the degradation of CR molecules in aqueous solution under solar irradiation. Nanofiltration (NF) performance in terms of CR residual removal from water and their fouling behavior during post-separation of photocatalysts was studied. Serious flux declined and thicker fouling layer on membrane were found in photocatalytic membrane reactor using Fe-doped ZnO/rGO NCs which could be attributed to the stronger π-π interaction between rGO and CR solution.
Common conventional biological treatment methods fail to decolorize palm oil mill effluent (POME). The present study focused on using the abundant palm oil mill boiler (POMB) ashes for POME decolorization. The POMB ashes were subjected to microwave irradiation and chemical treatment using H2SO4. The resultant adsorbents were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Brunauer-Emmett-Teller (BET) analyses. The adsorption efficiency was evaluated at various pH levels (2-8.5), adsorption dosages (3-15 g) in 200 mL, and contact times (1-5 h). The microwave-irradiated POMB-retained ash recorded the highest color removal of 92.31%, for which the best conditions were pH 2, 15 g adsorbent dosage in 200 mL, and 5 h of contact time. At these best treatment conditions, the color concentration of the treated effluent was analyzed using the method proposed by the American Dye Manufacturers Institute (ADMI). The color concentration was 19.20 ADMI, which complies with the Malaysia discharge standard class A. The Freundlich isotherm model better fit the experimental data and had a high R2 of 0.9740. Based on these results, it can be deduced that microwave-irradiated POMB-retained ash has potential applications for POME decolorization via a biosorption process.
An advanced electrodialysis fermentation system was set up to remove ammonium during hydrogen fermentation. When the voltage was increased from 0 to 6 V, the average ammonium removal rate was improved from 8.7 to 31.1 mg/L/h at an initial ammonium concentration of 3000 mg/L. A model based on the Nernst-Plank equation and porous media properties of ion exchange membranes was successfully implemented to predict the ammonium removal performance. When such a system was fed with synthetic wastewater at an ammonium concentration of 3000 mg/L for hydrogen fermentation, a significant increase in specific hydrogen yield was observed in the experiment group at 4 V. Specific hydrogen yield was 225.0 mL/g glucose, this value is 47.9% higher than the control. Moreover, ammonium concentration in experiment group was reduced to 701.6 mg/L at 72 h when voltage was set at 4 V, which is 63.7% lower than that in 0 V experiment group.
In this work, landfill leachate treatment by electrocoagulation process with a novel rotating anode reactor was studied. The influence of rotating anode speed on the removal efficiency of chemical oxygen demand (COD), total dissolved solids (TDS), and total suspended solids (TSS) of raw landfill leachate was investigated. The influence of operating parameters like leachate pH, leachate temperature, current, and inter-distance between the cathode rings and anode impellers on the electrocoagulation performance were also investigated. The results revealed the optimum rotating speed is 150 rpm and increasing the rotating speed above this value led to reducing process performance. The leachate electrocoagulation treatment process favors the neutral medium and the treatment performance increases with increasing current intensity. Furthermore, the electrocoagulation treatment performance improves with increasing leachate temperature. However, the performance reduces with increasing inter-electrode distance.
An Eulerian passive tracer model coupled with a quadruple-nested 3D circulation model was used to assess the coastal dispersal of treated wastewater effluent from a sewage treatment plant and the associated impacts on an adjacent seaweed farm using three different operational scenarios. When the discharged volume and source effluent fluxes were decreased by ~16.7%, the accumulated effluent in the farm was reduced by ~25.4%. A tracer flux budget analysis revealed the apparent predominance of the transient component that accounts for the nonlinear interactions primarily from tidal currents and eddies. The transient flux promoted the effluent influx to impede effluent accumulation in the farm, whereas the mean flux contributed to the outgoing flux. A source flux reduction caused a remarkable decrease in the transient flux and thus an even greater effluent accumulation reduction. In turn, a modified source density scenario without total effluent volume change did not work as expected.
In this present study, adsorptive membranes for Cr(VI) ion removal were prepared by blending polyethersulfone (PES) with hydrous ferric oxide (HFO) nanoparticles (NPs). The effects of HFO NPs to PES weight ratio (0-1.5) on the physicochemical properties of the resultant HFO/PES adsorptive membranes were investigated with respect to the surface chemistry and roughness as well as structural morphologies using different analytical instruments. The adsorptive performance of the HFO NPs/PES membranes was studied via batch adsorption experiments under various conditions by varying solution pH, initial concentration of Cr(VI), and contact time. The results showed that the membrane made of HFO/PES at a weight ratio of 1.0 exhibited the highest adsorption capacity which is 13.5 mg/g. Isotherm and kinetic studies revealed that the mechanism is best fitted to the Langmuir model and pseudo-second-order model. For filtration of Cr(VI), the best promising membranes showed improved water flux (629.3 L/m2 h) with Cr(VI) ion removal of 75%. More importantly, the newly developed membrane maintained the Cr(VI) concentration below the maximum contamination level (MCL) for up to 9 h.
One of the biggest challenges of using single-chamber microbial fuel cells (MFCs) that utilize proton-exchange membrane (PEM) air cathode for bioenergy recovery from recalcitrant organic compounds present in wastewater is mainly attributed to their high internal resistance in the anodic chamber of the single microbial fuel cell (MFC) configurations. The high internal resistance is due to the small surface area of the anode and cathode electrodes following membrane biofouling and pH splitting conditions as well as substrate and oxygen crossover through the membrane pores by diffusion. To address this issue, the fabrication of new PEM air-cathode single-chamber MFC configuration was investigated with inner channel flow open assembled with double PEM air cathodes (two oxygen reduction activity zones) coupled with spiral-anode MFC (2MA-CsS-AMFC). The effect of various proton-exchange membranes (PEMs), including Nafion 117 (N-117), Nafion 115 (N-115), and Nafion 212 (N-212) with respective thicknesses of 183, 127, and 50.08 μ, was separately incorporated into carbon cloth as PEM air-cathode electrode to evaluate their influences on the performance of the 2MA-CsS-AMFC configuration operated in fed-batch mode, while Azorubine dye was selected as the recalcitrant organic compound. The fed-batch test results showed that the 2MA-CsS-AMFC configuration with PEM N-115 operated at Azorubine dye concentration of 300 mg L-1 produced the highest power density of 1022.5 mW m-2 and open-circuit voltage (OCV) of 1.20 V coupled with enhanced dye removal (4.77 mg L h-1) compared to 2MA-CsS-AMFCs with PEMs N-117 and N-212 and those in previously published data. Interestingly, PEM 115 showed remarkable reduction in biofouling and pH splitting. Apart from that, mass transfer coefficient of PEM N-117 was the most permeable to oxygen (KO = 1.72 × 10-4 cm s-1) and PEM N-212 was the most permeable membrane to Azorubine (KA = 7.52 × 10-8 cm s-1), while PEM N-115 was the least permeable to both oxygen (KO = 1.54 × 10-4) and Azorubine (KA = 7.70 × 10-10). The results demonstrated that the 2MA-CsS-AMFC could be promising configuration for bioenergy recovery from wastewater treatment under various PEMs, while application of PEM N-115 produced the best performance compared to PEMs N-212 and N-117 and those in previous studies of membrane/membrane-less air-cathode single-chamber MFCs that consumed dye wastewater.
Despite efforts to address the composition of the microbial community during the anaerobic treatment of palm oil mill effluent (POME), its composition in relation to biodegradation in the full-scale treatment system has not yet been extensively examined. Therefore, a thorough analysis of bacterial and archaeal communities was performed in the present study using MiSeq sequencing at the different stages of the POME treatment, which comprised anaerobic as well as facultative anaerobic and aerobic processes, including the mixed raw effluent (MRE), mixing pond, holding tank, and final discharge phases. Based on the results obtained, the following biodegradation processes were suggested to occur at the different treatment stages: (1) Lactobacillaceae (35.9%) dominated the first stage, which contributed to high lactic acid production; (2) the higher population of Clostridiaceae in the mixing pond (47.7%) and Prevotellaceae in the holding tank (49.7%) promoted acetic acid production; (3) the aceticlastic methanogen Methanosaetaceae (0.6-0.8%) played a role in acetic acid degradation in the open digester and closed reactor for methane generation; (4) Syntrophomonas (21.5-29.2%) appeared to be involved in the degradation of fatty acids and acetic acid by syntrophic cooperation with the hydrogenotrophic methanogen, Methanobacteriaceae (0.6-1.3%); and (5) the phenols and alcohols detected in the early phases, but not in the final discharge phase, indicated the successful degradation of lignocellulosic materials. The present results contribute to a better understanding of the biodegradation mechanisms involved in the different stages of the full-scale treatment of POME.
Inaccessible hygiene water sources and sanitation are one of the sustainability issues that need to be solved. An attempt to solve this problem is to change the conventional system used in the water supply and sewage treatment to sustainable water and waste management. To transform the system, companies initially need to map their business value chain. However, this process is often not receiving a full attention by the organisation. In an academic perspective, there are limited studies that map the value chains of water and waste systems. To overcome this limitation, the present study aims to map the value chain processes of the water and wastewater utility companies towards a sustainability solution. A review of related studies is used to conduct this study. Khuzestan Urban Water and Sewage company in Iran has been selected as case studies. The mapping results indicate a lack of sustainability integration in a water management system that leads to ineffective and inefficient water management. Value chain mapping process is significant for practitioners, particularly in the water and sewage companies, as a starting point for transforming their conventional water management systems towards sustainability. Experts at the company stated that value chain mapping as part of value chain analysis enables organisations to increase operational efficiency and eliminate waste by 57%.
Despite being a key Malaysian economic contributor, the oil palm industry generates a large quantity of environmental pollutant known as palm oil mill effluent (POME). Therefore, the need to remediate POME has drawn a mounting interest among environmental scientists. This study has pioneered the application of Meyerozyma guilliermondii with accession number (MH 374161) that was isolated indigenously in accessing its potential to degrade POME. This strain was able to treat POME in shake flask experiments under aerobic condition by utilising POME as a sole source of carbon. However, it has also been shown that the addition of suitable carbon and nitrogen sources has significantly improved the degradation potential of M. guilliermondii. The remediation of POME using this strain resulted in a substantial reduction of chemical oxygen demand (COD) of 72%, total nitrogen of 49.2% removal, ammonical nitrogen of 45.1% removal, total organic carbon of 46.6% removal, phosphate of 60.6% removal, and 92.4% removal of oil and grease after 7 days of treatment period. The strain also exhibited an extracellular lipase activity which promotes better wastewater treatment. Additionally, Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) analyses have specifically shown that M. guilliermondii strain can degrade hydrocarbons, fatty acids, and phenolic compounds present in the POME. Ultimately, this study has demonstrated that M. guilliermondii which was isolated indigenously exhibits an excellent degrading ability. Therefore, this strain is suitable to be employed in the remediation of POME, contributing to a safe discharge of the effluent into the environment.