Industrialization and overpopulation have polluted aquatic environments with significant impacts on human health and wildlife. The main pollutants in urban sewage are nitrogen, phosphorus, heavy metals and organic pollutants, which need to be treated with sewage, and the use of aquatic plants to purify wastewater has high efficiency and low cost. However, the effectiveness and efficiency of phytoremediation are also affected by temperature, pH, microorganisms and other factors. The use of biochar can reduce the cost of wastewater purification, and the combination of biochar and nanotechnology can improve the efficiency of wastewater purification. Some aquatic plants can enrich pollutants in wastewater, so it can be considered to plant these aquatic plants in constructed wetlands to achieve the effect of purifying wastewater. Biochar treatment technology can purify wastewater with high efficiency and low cost, and can be further applied to constructed wetlands. In this paper, the latest research progress of various pollutants in wastewater purification by aquatic plants is reviewed, and the efficient treatment technology of wastewater by biochar is discussed. It provides theoretical basis for phytoremediation of urban sewage pollution in the future.
Agro-industrial biorefinery effluent (AIBW) is considered a highly polluting source responsible for environmental contamination. It contains high loads of chemical oxygen demand (COD), and phenol, with several other organic and inorganic constituents. Thus, an economic treatment approach is required for the sustainable discharge of the effluent. The long-term process performance, contaminant removal and microbial response of AIBW to rice straw-based biochar (RSB) and biochar-based geopolymer nanocomposite (BGC) as biosorbents in an activated sludge process were investigated. The adsorbents operated in an extended aeration system with a varied hydraulic retention time of between 0.5 and 1.5 d and an AIBW concentration of 40-100% for COD and phenol removal under standard conditions. Response surface methodology was utilised to optimize the process variables of the bioreactor system. Process results indicated a significant reduction of COD (79.51%, 98.01%) and phenol (61.94%, 74.44%) for BEAS and GEAS bioreactors respectively, at 1 d HRT and AIBW of 70%. Kinetic model analysis indicated that the Stover-Kincannon model best describes the system functionality, while the Grau model was better in predicting substrate removal rate and both with a precision of between R2 (0.9008-0.9988). Microbial communities examined indicated the abundance of genera, following the biosorbent addition, while RSB and BGC had no negative effect on the bioreactor's performance and bacterial community structure of biomass. Proteobacteria and Bacteroidetes were abundant in BEAS. While the GEAS achieved higher COD and phenol removal due to high Nitrosomonas, Nitrospira, Comamonas, Methanomethylovorans and Acinetobacter abundance in the activated sludge. Thus, this study demonstrated that the combination of biosorption and activated sludge processes could be promising, highly efficient, and most economical for AIBW treatment, without jeopardising the elimination of pollutants or the development of microbial communities.
In an effort to seek a new technical platform for disposal of drinking water treatment sludge (DWTS: alum sludge), pyrolysis of DWTS was mainly investigated in this study. To establish a more sustainable thermolytic platform for DWTS, this study particularly employed CO2 as reactive gas medium. Thus, this study laid great emphasis on elucidating the mechanistic roles of CO2 during the thermolysis of DWTS. A series of the TGA tests of DWTS in CO2 in reference to N2 revealed no occurrence of the heterogeneous reaction between CO2 and the sample surface of DWTS. As such, at the temperature regime before initiating the Boudouard reaction (i.e., ≥700 °C), the mass decay patterns of DWTS in N2 and CO2 were nearly identical. However, the gaseous effluents from lab-scale pyrolysis of DWTS in CO2 in reference to N2 were different. In sum, the homogeneous reactions between CO2 and volatile matters (VMs) evolved from the thermolysis of DWTS led to the enhanced generation of CO. Also, CO2 suppressed dehydrogenation of VMs. Such the genuine mechanistic roles of CO2 in the thermolysis of DWTS subsequently led to the compositional modifications of the chemical species in pyrolytic oil. Furthermore, the biochar composite was obtained as byproduct of pyrolysis of DWTS. Considering that the high content of Al2O3 and Fe-species in the biochar composite imparts a strong affinity for As(V), the practical use of the biochar composite as a sorptive material for arsenic (V) was evaluated at the fundamental levels. This work reported that adsorption of As(V) onto the biochar composite followed the pseudo-second order model and the Freundlich isotherm model.
Bioelectrochemical sensors for environment monitoring have the potential to provide facility operators with real-time data, allowing for better and more timely decision-making regarding water and wastewater treatment. To assess the robustness and sensitivity of the Sentry™ biosensor in local conditions, it was tested in Malaysia using domestically available wastewater. The study objectives included (1) enrich the biosensor locally, (2) operate and test the biosensor with local domestic wastewater, and (3) determine the biosensor's responsiveness to model pollutants through pollutant spike and immersion test as well as response to absence of wastewater. Lab-scale operation shows the biosensor was successfully enriched with (1) local University Kebangsaan Malaysia's, microbial community strain collection and (2) local municipal wastewater microflora, operated for more than 50 days with a stable yet responsive carbon consumption rate (CCR) signal. Meanwhile, two independent biosensors were also enriched and operated in Indah Water Research Centre's crude sewage holding tank, showing a stable response to the wastewater. Next, a pilot scale setup was constructed to test the enriched biosensors for the spiked-pollutant test. The biosensors showed a proportional CCR response (pollutant presence detected) towards several organic compounds in the sewage, including ethanol, chicken blood, and dilution of tested sewage but less to curry powder, methanol, and isopropanol. Conversely, there was no significant response (pollutant presence not detected) towards hexane, Congo red, engine oil, and paint, which may be due to their non-biodegradability and/or insoluble nature. Additionally, the biosensors were exposed to air for 6 h to assess their robustness towards aerobic shock with a positive result. Overall, the study suggested that the biosensor could be a powerful monitoring tool, given its responsiveness towards organic compounds in sewage under normal conditions.
In this study, pyrolysis technique was utilized for converting palm oil sludge to value added materials: bio-oil (liquid fuel) and bio-char (soil amendment). The bio-oil yield obtained was 27.4±1.7 wt.% having a heating value of 22.2±3.7 MJ/kg and a negligible ash content of 0.23±0.01 wt.%. The pH of bio-oil was in alkaline region. The bio-char yielded 49.9±0.3 wt.%, which was further investigated for sorption efficiency by adsorbing metal (Cd(2+) ions) from water. The removal efficiency of Cd(2+) was 89.4±2%, which was almost similar to the removal efficiency of a commercial activated carbon. The adsorption isotherm was well described by Langmuir model. Therefore, pyrolysis is proved as an efficient tool for palm oil sludge management, where the waste was converted into valuable products.
Aerobic granular sludge (AGS) has been applied to treat a broad range of industrial and municipal wastewater. AGS can be developed in a sequencing batch reactor (SBR) with alternating anaerobic-aerobic conditions. To provide anaerobic conditions, the mixed liquor is allowed to circulate in the reactor without air supply. The circulation flow rate of mixed liquor in anaerobic condition is the most important parameter of operation in the anaerobic-AGS processes. Therefore, this study investigates the effect of circulation rate on the performance of the SBR with AGS. Two identical reactors namely R1 and R2 were operated using fermented soy sauce wastewater at circulation rate of 14.4 and 36.0 l/h, respectively. During the anaerobic conditions, the wastewater was pumped out from the upper part of the reactor and circulated back into the bottom of the reactor for 230 min. A compact and dense AGS was observed in both reactors with a similar diameter of 2.0 mm in average, although different circulation rates were adopted. The best reactor performance was achieved in R2 with chemical oxygen demand removal rate of 89%, 90% total phosphorus removal, 79% ammonia removal, 10.1 g/l of mixed liquor suspended solids and a sludge volume index of 25 ml/g.
A green technology of biodiesel production focuses on the use of enzymes as the catalyst. In enzymatic biodiesel synthesis, suitable solvent system is very essential to reduce the inhibition effects of the solvent to the enzymes. This study produced ethanol-based biodiesel from a low-cost sludge palm oil (SPO) using locally-produced Candida cylindracea lipase from fermentation of palm oil mill effluent (POME) based medium. The optimum levels of ethanol-to-SPO molar ratio and enzyme loading were found to be 4:1 and 10 U/25 g of SPO respectively with 54.4% w/w SPO yield of biodiesel and 21.7% conversion of free fatty acid (FFA) into biodiesel. Addition of tert-butanol at 2:1 tert-butanol-to-SPO molar ratio into the ethanol-solvent system increased the yield of biodiesel to 71.6% w/w SPO and conversion of FFA into biodiesel to 28.8%. The SPO and ethanol have promising potential for the production of renewable biodiesel using enzymatic-catalyzed esterification and transesterification.
Optimization of thermo-alkaline disintegration of sewage sludge for enhanced biogas yield was carried out using response surface methodology (RSM) and Box-Behnken design of experiment. The individual linear and quadratic effects as well as the interactive effects of temperature, NaOH concentration and time on the degree of disintegration were investigated. The optimum degree of disintegration achieved was 61.45% at 88.50 °C, 2.29 M NaOH (24.23%w/w total solids) and 21 min retention time. Linear and quadratic effects of temperature are most significant in affecting the degree of disintegration. The coefficient of determination (R(2)) of 99.5% confirms that the model used in predicting the degree of disintegration process has a very good fitness with the experimental variables. The disintegrated sludge increased the biogas yield by 36%v/v compared to non-disintegrated sludge. The RSM with Box-Behnken design is an effective tool in predicting the optimum degree of disintegration of sewage sludge for increased biogas yield.
In this study, solidification/stabilization (S/S) of nickel hydroxide sludge using ordinary Portland cement (OPC) and oil palm ash (OPA) was carried out. The effects of increased substitution of OPA wt% in the S/S mix designs on the treated samples' physical and chemical characteristics were investigated. The physical characteristics studied were unconfined compressive strength (UCS) and changes in crystalline phases while chemical characteristics studied were leachability of nickel and leachate pH. Results indicated the optimum mix design for S/S of nickel hydroxide sludge using both OPC and OPA at B/S(d)=1 in terms of cost-effectiveness and treatment efficiency was 15 wt% OPA, 35 wt% OPC and 50 wt% sludge. The sufficient UCS and low leached nickel concentrations shown for this mix design indicate the viability of using OPA as substitute of OPC as it can significantly reduce cost normally incurred by usage of high amounts of OPC.
The production of methanol from agricultural, forestry, livestock, poultry, and fishery waste via pyrolysis was investigated. Pyrolysis was conducted in a tube furnace at 450-500 °C. Sugarcane bagasse showed the methanol production (5.93 wt.%), followed by roots and sawdust with 4.36 and 4.22 wt.%, respectively. Animal waste offered the lowest content of methanol, as only 0.46, 0.80, and 0.61 wt.% were obtained from fishery, goat, and cow waste, respectively. It was also observed that the percentage of methanol increased with an increase in volatile compounds while the percentage of ethanol increased with the percentage of ash and fix carbon. The data indicate that, pyrolysis is a means for production of methanol and ethanol after further optimization of the process and sample treatment.
Land application of sludge as fertilizers is a way of disposal and recycling of sludge. However, public concern has arisen due to the fact that organic contaminants in sludge may ultimately enter the food chain. Hence the need arises to analyse the organic contaminants such as PAHs and OCPs in sludge. In this study, Soxhlet was utilised as the extraction method and the extracts subjected to extensive cleanup via either silica columns or solid phase extraction cartridges prior to analysis using gas chromatography or high performance liquid chromatography. Sludge samples were collected from the drying beds of oxidation ponds in three locations in South Johore. OCPs such as heptachlor, dieldrin and pp-DDT were detected in low amounts (52-159 mg/kg) whereas PAHs such as naphthalene, phenanthrene, fluoranthene and benzo(a)pyrene were detected in the range of 0.2-5.5 mg/kg dry mass. Subcritical water extraction (SWE) recovery studies of PAHs were also performed from spiked sludge samples. Although a recovery range of 41-68% was obtained using the SWE method, the results indicated the usefulness of the technique as an alternative to Soxhlet extraction for the analysis of PAHs in sludge samples.
A laboratory-scale study was undertaken to evaluate the liquid state bioconversion (LSB) in terms of biodegradation of microbially treated domestic wastewater sludge (biosolids) as well as its kinetics. The potential fungal strains and process factors developed from previous studies were used throughout the study. The results presented in this study showed that an effective biodegradation occurred with the biosolids (sludge cake) accumulated. The maximum biosolids (sludge cake) accumulated (93.8 g/kg of liquid sludge) enriched with the biomass protein (30.2 g/kg of dry biosolids), was achieved which improved the effluent quality by enhancing the removal of chemical oxygen demand (COD), reducing sugar (RS), soluble protein (SP), total dissolved solids (TDS), and total suspended solids (TSS). The higher reduction of specific resistance to filtration (SRF) was observed during bioconversion process. The kinetics results showed that the experimental data were better fitted for the biodegradation efficiency, and biosolids accumulation and biodegradation rate.
Experiments were conducted to remove heavy metals (Cr, Cd, Pb, Cu and Zn) from urban sewage sludge (SS) amended with spent mushroom compost (SMC) using worms, Lumbricus rubellus, for 105 days, after 21 days of pre-composting. Five combinations of SS/SMC treatments were prepared in triplicate along with a control for each treatment in microcosms. Analysis of the earthworms' multiplication and growth and laboratory analysis were conducted during the tenth and fifteenth week of vermicomposting. Our result showed that the final biomass of earthworms (mg) and final number of earthworms showed significant differences between treatments i.e. F=554.70, P=0.00 and F=729.10, P=0.00 respectively. The heavy metals Cr, Cd and Pb contained in vermicompost were lower than initial concentrations, with 90-98.7 percent removal on week ten. However, concentrations of Cu and Zn, that are considered as micronutrients, were higher than initial concentrations, but they were 10-200-fold lower than the EU and USA biosolid compost limits and Malaysian Recommended Site Screening Levels for Contaminated Land (SSLs). An increment of heavy metals were recorded in vermicompost for all treatments on week fifteen compared to week ten, while concentration of heavy metals in earthworms' tissue were lower compared to vermicompost. Hence, it is suggested that earthworms begin to discharge heavy metals into their surroundings and it was evident that the earthworms' heavy metals excretion period was within the interval of ten to fifteen weeks.
A two-stage anoxic transformation process, involving growth of biomass utilizing two types of different electron acceptors, namely nitrate and nitrite, has been observed. The present water quality modules established for sewer processes cannot account for the two-stage process. This paper outlines the development of a model concept that enables the two-stage anoxic transformation process to be simulated. The proposed model is formulated in a matrix form that is similar to the Activated Sludge Models and Sewer Process Model matrices. The model was successfully applied to simulate changes in nitrate and nitrite concentrations during anoxic transformations in the bulkwater phase of municipal wastewater.
Water pollution during festival periods is a major problem in all festival cities across the world. Reliable prediction of water pollution is essential in festival cities for sewer and wastewater management in order to ensure public health and a clean environment. This article aims to model the biological oxygen demand (BOD(5)), and total suspended solids (TSS) parameters in wastewater in the sewer networks of Karbala city center during festival and rainy days using structural equation modeling and multiple linear regression analysis methods. For this purpose, 34 years (1980-2014) of rainfall, temperature and sewer flow data during festival periods in the study area were collected, processed, and employed. The results show that the TSS concentration increases by 26-46 mg/l while BOD(5) concentration rises by 9-19 mg/l for an increase of rainfall by 1 mm during festival periods. It was also found that BOD(5) concentration rises by 4-17 mg/l for each increase of 10,000 population.
With inoculum sludge from a conventional activated sludge wastewater treatment plant, three sequencing batch reactors (SBRs) fed with synthetic wastewater were operated at different high temperatures (30, 40 and 50±1°C) to study the formation of aerobic granular sludge (AGS) for simultaneous organics and nutrients removal with a complete cycle time of 3h. The AGS were successfully cultivated with influent loading rate of 1.6CODg(Ld)(-1). The COD/N ratio of the influent wastewater was 8. The results revealed that granules developed at 50°C have the highest average diameter, (3.36mm) with 98.17%, 94.45% and 72.46% removal efficiency observed in the system for COD, ammonia and phosphate, respectively. This study also demonstrated the capabilities of AGS formation at high temperatures which is suitable to be applied for hot climate conditions.
This study was conducted to evaluate the effect of an eminent decay fungus, Phanerocheate chrysosporium of organic residues on wastewater sludge for its improvement through decomposition and separation of waste particles by Liquid State Bioconversion (LSB). The effect of fungal treatment was compared to uninoculated (Control) at three different harvests 7, 14 and 21 days after inoculation (DAI). The observed results showed that the weight loss and solid content of wastewater sludge were significantly influenced by Phanerocheate chrysosporium. Both parameters were highly influenced at 7 DAI. The COD and pH of wastewater sludge were also highly influenced by fungal treatment.
Sewage sludge from aerobic treatment plant was found to contain high amounts of heavy metals. Research was carried out to investigate the speciation and leaching behavior of heavy metals when using high temperature melting technology for treatment. This was achieved by conducting a sequential chemical extraction procedure and EP-TOX leaching test. The thermal treatment led to increased shift of metals from organic fraction to residual fraction, indicating that the thermal treatment caused metals in sewage sludge to become stable. Furthermore, results from leaching test revealed that metals were not leached from the final product after thermal treatment and this was verified using US EPA standard limits. Results from this study indicated that melting technology could convert the sludge to product that can be either reused or landfilled without an adverse environmental impact.
The sorption of Cu(II) and Cd(II) from synthetic solution by powdered activated carbon (PAC), biomass, rice husk (RH) and activated rice husk (ARH) were investigate under batch conditions. After activated by concentrated nitric acid for 15 hours at 60-65 degrees C, the adsorption capacity for RH was increased. The adsorbents arranged in the increasing order of adsorption capacities to the Langmuir Q degree parameter were biomass > PAC > ARH > RH. The addition of adsorbents in base mix solution had increased the specific oxygen uptake rate (SOUR) activated sludge microorganisms with and without the presence of metals. The increased of SOUR were due to the ability of PAC and RH in reducing the inhibitory effect of metals on microorganisms and provide a reaction site between activated sludge microorganisms and substrates.
Pulau Redang and Pulau Tioman have experienced huge tourism growth over the last two decades, but minimal sewage treatment may threaten the resilience of their coral reefs. This study uses stable isotope techniques to identify suitable bioindicators of sewage nutrients (δ15N) at these islands by measuring macroalgae (Lobophora spp.), gastropods (Drupella spp.), scleractinian coral (Acropora spp.), and leather coral (Sinularia spp.). At tourist hubs using seepage septic tank systems, enrichment of Acropora δ15N (Redang, +0.7‰) and Sinularia δ15N (Tioman, +0.4‰) compared to pristine background levels indicate enhanced sewage nutrient discharge. Carbon isotopes and survey data suggest that sedimentation did not confound these δ15N trends. Potential damaging effects of sewage discharge on the coral reef communities at both islands are highlighted by strong correlations between Acropora δ15N and regional variation in coral reef community structure, and exclusive occurrence of degraded reefs at regions of high sewage influence.