A study was conducted to investigate the efficiency of coagulation and flocculation processes for removing colour from a semi-aerobic landfill leachate from one of the landfill sites in Malaysia. Four types of coagulant namely aluminium (III) sulphate (alum), ferric (III) chloride, ferrous (II) sulphate and ferric (III) sulphate were studied using standard jar test apparatus. Results indicated that ferric chloride was superior to the other coagulants and removed 94% of colour at an optimum dose of 800 mg/l at pH 4. The effect of coagulant dosages on colour removal showed similar trend as for COD, turbidity and suspended solids. This suggested that colour in landfill leachate was mainly contributed by organic matters with some insoluble forms that exhibited turbidity and suspended solids readings. The results from this study suggested that ferric chloride could be a viable coagulant in managing colour problems associated with landfill leachate.
Microcystins-LR (MC-LR) which is a kind of potent hepatotoxin for humans and wildlife can be biodegraded by microbial community. In this study, the capacity of biofilm in degrading MC-LR was investigated with and without additional metal ions (Mn(2+), Zn(2+) and Cu(2+)) at the concentration of 1 mg L(-1). The results indicated that the degradation rate of MC-LR by biofilm was inhibited by introduced Mn(2+) and Cu(2+) during the whole culture period. MC-LR cannot be degraded until a period of culture time passed both in the cases with Zn(2+) and Cu(2+) (2 and 8 days for Zn(2+) and Cu(2+), respectively). The results of mlrA gene analysis showed that the abundance of MC-LR degradation bacteria (MCLDB) in the microbial community under Mn(2+) condition was generally lower than that under no additional metal ion condition. Meanwhile, a two days lag phase for the proliferation of MCLDB occurred after introducing Zn(2+). And a dynamic change of MCLDB from Cu(2+) inhibited species to Cu(2+) promoted species was observed under Cu(2+) condition. The maximum ratio of MCLDB to overall bacteria under various conditions during culture process was found to follow the tendency as: Cu(2+) > Zn(2+) ≈ no additional metal ion (Control) > Mn(2+), suggesting the adverse effect of Mn(2+), no obvious effect of Zn(2+) and positive effect of Cu(2+) on the distribution ratio of MCLDB over the biofilm.
The production of natural biopolymers as flocculants for water treatment is highly desirable due to their inherent low toxicity and low environmental footprint. In this study, bio-flocculants were extracted from Hibiscus/Abelmoschus esculentus (okra) by using a water extraction method, and the extract yield and its performance in sludge dewatering were evaluated. Single factor experimental design was employed to obtain the optimum conditions for extraction temperature (25-90 °C), time (0.25-5 h), solvent loading (0.5-5 w/w) and agitation speed (0-225 rpm). Results showed that extraction yield was affected non-linearly by all experimental variables, whilst the sludge dewatering ability was only influenced by the temperature of the extraction process. The optimum extraction conditions were obtained at 70 °C, 2 h, solvent loading of 2.5 w/w and agitation at 200 rpm. Under the optimal conditions, the extract yield was 2.38%, which is comparable to the extraction of other polysaccharides (0.69-3.66%). The bio-flocculants displayed >98% removal of suspended solids and 68% water recovery during sludge dewatering, and were shown to be comparable with commercial polyacrylamide flocculants. This work shows that bio-flocculants could offer a feasible alternative to synthetic flocculants for water treatment and sludge dewatering applications, and can be extracted using only water as a solvent, minimising the environmental footprint of the extraction process.
An innovative design of upflow constructed wetland-microbial fuel cell (UFCW-MFC) planted with cattail was used for simultaneous wastewater treatment and electricity generation. The electrodes material employed in the study was carbon felt. The main aim of this study is to assess the performance of the UFCW coupling with MFC in term of ability to treat wastewater and the capability to generate bioelectricity. The oxidation reduction potential (ORP) and dissolved oxygen (DO) profile showed that the anaerobic and aerobic regions were well developed in the lower and upper bed, respectively, of UFCW-MFC. Biodegradation of organic matter, nitrification and denitrification was investigated and the removal efficiencies of COD, NO3(-), NH4(+) were 100%, 40%, and 91%, respectively. The maximum power density of 6.12 mW m(-2) and coulombic efficiency of 8.6% were achieved at electrode spacing of anode 1 (A1) and cathode (15 cm).
Application of ozonation in water treatment involves complex oxidation pathways that could lead to the formation of various by-products, some of which may be harmful to living organisms. In this work, ozonation by-products of ofloxacin (OFX), a frequently detected pharmaceutical pollutant in the environment, were identified and their ecotoxicity was estimated using the Ecological Structure Activity Relationships (ECOSAR) computer program. In order to examine the role of ozone (O3) and hydroxyl radicals (∙OH) in the degradation of ofloxacin, ozonation was performed at pH2, 7 and 12. In this study, 12 new structures have been proposed for the ozonation by-products detected during the ozonation of ofloxacin. According to the identified ozonation by-products, O3 and ∙OH were found to react with ofloxacin during ozonation. The reaction between ofloxacin and O3 proceeded via hydroxylation and breakdown of heterocyclic ring with unsaturated double-bond. The reaction between ofloxacin and ·OH generated various by-products derived from the breakdown of heterocyclic ring. Ecotoxicity assessment indicated that ozonation of OFX could yield by-products of greater toxicity compared with parent compounds.
Several types of water treatment technologies including adsorption are now being used to treat polluted water. In this paper the removal of phenol by adsorption will be discussed. Activated carbons are successfully applied for purification of potable water and the removal of organic pollutants in wastwater. This paper is concerned with a low cost approach to treating waste water that is significant especially for those countries where oil palm is an available agricultural product like Malaysia, Ivory Coast, Nigeria, Thailand, Papua New Guinea. In the coastal region coconut is an available agricultural product and activated carbon prepared using coconut shell is also an economical method of water treatment. The materials used in this study were Commercial Activated Carbon (CAC), prepared from coconut shell and Modified Oil Palm Shell (MOPAS) of 1 to 2 mm diameters. The surface area of CAC and MOPAS was 38.5 m2/g and 38.2 m2/g respectively and the iodine number was determined as 674 and 454 for CAC and MOPAS, respectively. From the study the result shows above 70% removal efficiency for 5 mg/L and 40% removal efficiency for 20 mg/L of phenol solution. The performance efficiency will be discussed based on batch test, following Freundlich adsorption isotherm. The results indicate that CAC exhibits a higher adsorptive capacity (Kf of 0.079) as compared to MOPAS (Kf of 0.048). Hence a better removal efficiency for CAC at lower concentration of phenol. Results from column tests show a better adsorptive capacity for CAC (2.73) as compared to MOPAS (2.48).
A laboratory-scale membrane bioreactor (MBR) was fed with synthetic wastewater to investigate the possibility of simultaneous removal of organic, nitrogen and phosphorus by intermittent aeration. The MBR consists of two compartments using a microfiltration membrane with 0.2 microm pore size and a surface area of 0.35 m2. Hydraulic retention time was set at 24 hours and solid retention time 25 days. MLSS concentration in the reactor was in the range of 2,500-3,800 mg/L. The MLSS internal recycling ratio was maintained at 100% influent flow rate. Intermittent aeration was applied in this study to provide an aerobic-anaerobic cycle. Three stages of operations were conducted to investigate the effect of aeration and non-aeration on simultaneous organic and nutrient removal. In Stage 1, time cycles of aeration and non-aeration were set at 90/150 min and 150/90 min in the first and second compartment, the removal efficiency was 97%, 94% and 70% for COD, nitrogen and phosphorus respectively. In Stage 2, time cycles of aeration and non-aeration were set at 60/120 min and 120/60 min in the first and second compartment, the removal efficiency was 97%, 96% and 71% for COD, nitrogen and phosphorus respectively. In Stage 3, time cycles of aeration and non-aeration were set at 120/120 min and 120/120 min in compartment 1 and 2, the removal efficiency was 98%, 96% and 78% for COD, nitrogen and phosphorus respectively. Results show that longer non-aeration time in the second compartment provided better performances of biological phosphorus removal.
Environmental monitoring was carried out at Upper Layang Reservoir situated in Masai, Johor, Malaysia. The study shows that thermal stratification and natural mixing of the water column do exist in the reservoir and the level of stratification varies at different times of the year. Artificial destratification via diffused air aeration techniques was employed at the reservoir for two months. The results show that thermal stratification was eliminated after a week of continuous aeration. The concentrations of iron and to a lesser extent manganese in the water column was also reduced during the aeration period.
The removal of natural organic matter (NOM) using a continuous flow fixed bed granular activated carbon (GAC) column was studied and the results were then fitted with the Adams-Bohart, Bed-Depth-Service-Time and Clarks models. The GAC, KI-6070 and KI-8085 used in the study had external surface areas of 277 m2/g and 547 m2/g, respectively. Adsorption of NOM by the GAC was complex and involved more than one rate-limiting step. The critical bed depths for KI-6070 and KI-8085 were 0.24 m and 0.3 m, respectively. The Clark model was more effective in simulating the absorbent breakthrough process as compared to the Adams-Bohart model. The lower empty bed contact time (EBCT) i.e. 15 minutes gave a better fit to the Clark Model as compared to EBCT of 20 and 30 minutes.
The sewer is an integral part of the urban wastewater system: the sewer, the wastewater treatment plant and the local receiving waters. The sewer is a reactor for microbial changes of the wastewater during transport, affecting the quality of the wastewater and thereby the successive treatment processes or receiving water impacts during combined sewer overflows. This paper presents the results of studies on anoxic processes, namely denitrification, in the bulk water phase of wastewater as it occurs in sewers. Experiments conducted on 12 different wastewater samples have shown that the denitrification process in the bulk wastewater can be simplified by the reduction of nitrate to nitrogen with significant accumulation of nitrite in the water phase. Utilization of nitrate was observed not to be limited by nitrate for concentrations above 5 gNO3-N/m3. The denitrification rates, under conditions of excess substrate and electron acceptor, were found to be in the range of 0.8-2.0 g NO3-N/(m3h). A discussion on the interaction of the sewer processes and the effects on a downstream located wastewater treatment plant (WWTP) is provided.
The equilibrium sorption capacity of a macro-fungi, Pycnoporus sanguineus biomass was studied using a single-metal system comprising copper ions. The rate and extent for the removal of copper were subjected to environmental parameters such as pH, biomass loading, temperature, and contact time. Results showed that the uptake of copper increased as the pH increased. However, as the biomass loading increased, the amount of metal uptake decreased. Instead, temperature does not have a significant effect on the metal uptake, especially between 30 to 40 degrees C. A maximum adsorption of copper ions was also observed within 15 minutes of reaction time for the entire sample tested. Furthermore, pre-treatment with sodium bicarbonate and boiling water significantly improved the sorption capacity of copper by Pycnoporus sanguineus.
The adsorption of Cu(II) ions from aqueous solution by chitosan and chitosan/PVA beads was studied in a batch adsorption system. Chitosan solution was blended with poly(vinyl alcohol) (PVA) in order to obtain sorbents that are insoluble in aqueous acidic and basic solution. The adsorption capacities and rates of Cu(II) ions onto chitosan and chitosan/PVA beads were evaluated. The Langmuir, Freundlich and BET adsorption models were applied to describe the isotherms and isotherm constants. Adsorption isothermal data could be well interpreted by the Langmuir model. The kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the chemical sorption is the rate-limiting step. The Cu(II) ions can be removed from the chitosan and chitosan/PVA beads rapidly by treatment with an aqueous EDTA solution. Results also showed that chitosan and chitosan/PVA beads are favourable adsorbers.
The occurrence of various micropollutants such as pharmaceuticals personal care products, endocrine disrupting chemicals (PPCPs/EDCs) and metals in municipal wastewater, and their poor removal efficiencies can lead to toxicity impact on humans, and freshwater and terrestrial ecosystems. Life cycle assessment is an efficient and effective tool to evaluate the environmental impact of wastewater treatment plants, but guidelines for toxicity assessment are lacking due to the complexity. This study aims to evaluate both life cycle inventory by including metals and PEC, and life cycle toxicity assessment (LCIA) methods namely CML-IA, Recipe, USEtox, EDIP 2003 and IMPACT 2002+ in midpoint category with a large centralised wastewater treatment plant in Malaysia as a case study. The removal efficiencies of metals and PPCPs/EDCs in the wastewater ranged from 9% to 99% and no clear patterns were found about occurrence and removal efficiencies of metals and PPCPs/EDCs in developing and developed countries. The inclusion of metals and PPCPs/EDCs in effluent resulted in 76% increase in freshwater ecotoxicity potential (FEP) and 88% increase in terrestrial ecotoxicity potential (TEP) while only 4% increase in human toxicity potential (HTP). The results indicate the importance of including direct emissions such as metals and PPCPs/EDCs even in low-strength municipal wastewater for environmental toxicity assessment. The comparison of five LCIA methods suggests that HTP assessment is more challenging due to inconsistency between five LCIA methods while CML-IA, Recipe, and IMPACT 2002+ achieved consistent human toxicity and ecotoxicity assessment results in the WWTP. The results highlight the importance of sampling and inclusion of metals and PPCPs/EDCs data especially prioritised micropollutants for life cycle toxicity assessment and recommends LCIA methods for ecotoxicity assessment of WWTPs in the current scientific development situation on toxicity studies, which can provide guidance to researchers for life cycle toxicity assessment of wastewater treatment.
Efforts to improve water quality have led to the development of green and sustainable water treatment approaches. Herein, nitrogen-doped magnetized hydrochar (mSBHC-N) was synthesized, characterized, and used for the removal of post-transition and transition heavy metals, viz. Pb2+ and Cd2+ from aqueous environment. mSBHC-N was found to be mesoporous (BET surface area - 62.5 m2/g) and paramagnetic (saturation magnetization - 44 emu/g). Both, FT-IR (with peaks at 577, 1065, 1609 and 3440 cm-1 corresponding to Fe - O stretching vibrations, C - N stretching, N - H in-plane deformation and stretching) and XPS analyses (with peaks at 284.4, 400, 530, 710 eV due to C 1s, N 1s, O 1s, and Fe 2p) confirmed the presence of oxygen and nitrogen containing functional groups on mSBHC-N. The adsorption of Pb2+ and Cd2+ was governed by oxygen and nitrogen functionalities through electrostatic and co-ordination forces. 75-80% of Pb2+ and Cd2+ adsorption at Co: 25 mg/L, either from deionized water or humic acid solution was accomplished within 15 min. The data was fitted to pseudo-second-order kinetic and Langmuir isotherm models, with maximum monolayer adsorption capacities being 323 and 357 mg/g for Cd2+and Pb2+ at 318 K, respectively. Maximum Cd2+ (82.6%) and Pb2+ (78.7%) were eluted with 0.01 M HCl, simultaneously allowing minimum iron leaching (2.73%) from mSBHC-N. In conclusion, the study may provide a novel, economical, and clean route to utilize agro-waste, such as sugarcane bagasse (SB), for aquatic environment remediation.
Multi-walled carbon nanotubes (CNTs) functionalized with a deep eutectic solvent (DES) were utilized to remove mercury ions from water. An artificial neural network (ANN) technique was used for modelling the functionalized CNTs adsorption capacity. The amount of adsorbent dosage, contact time, mercury ions concentration and pH were varied, and the effect of parameters on the functionalized CNT adsorption capacity is observed. The (NARX) network, (FFNN) network and layer recurrent (LR) neural network were used. The model performance was compared using different indicators, including the root mean square error (RMSE), relative root mean square error (RRMSE), mean absolute percentage error (MAPE), mean square error (MSE), correlation coefficient (R2) and relative error (RE). Three kinetic models were applied to the experimental and predicted data; the pseudo second-order model was the best at describing the data. The maximum RE, R2 and MSE were 9.79%, 0.9701 and 1.15 × 10-3, respectively, for the NARX model; 15.02%, 0.9304 and 2.2 × 10-3 for the LR model; and 16.4%, 0.9313 and 2.27 × 10-3 for the FFNN model. The NARX model accurately predicted the adsorption capacity with better performance than the FFNN and LR models.
Comparison studies in suspension and hybrid photocatalytic membrane reactor (HPMR) system was investigated by using Reactive Black 5 (RB5) as target pollutant under UVA light irradiation. To achieve this aim, hybrid TiO2/clinoptilolite (TCP) photocatalyst powder was prepared by solid-state dispersion (SSD) methods and embedded at the outer layer of dual layer hollow fiber (DLHF) membranes fabricated via single step co-spinning process. TiO2 and CP photocatalyst were also used as control samples. The samples were characterized by Scanning Electron Microscopy (SEM), Energy Dispersion of X-ray (EDX), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) analyses. The result shows that TCP was actively functioned as photocatalyst in suspension system and 86% of RB5 photocatalytic degradation achieved within 60 min; however the additional step is required to separate the catalyst with treated water. In the HPMR system, even though the RB5 photocatalytic degradation exhibits lower efficiency however the rejection of RB5 was achieved up to 95% under UV irradiation due to the properties of photocatalytic membranes. The well dispersed of TCP at the outer layer of DLHF membrane have improved the surface affinity of DL-TCP membrane towards water, exhibit the highest pure water flux of 41.72 L/m2.h compared to DL-TiO2 membrane. In general, CP can help on improving photocatalytic activity of TiO2 in suspension, increased the RB5 removal and the permeability of DLHF membrane in HPMR system as well.
As cobalt (Co) represents an effective transition metal for activating Oxone to degrade contaminants, tricobalt tetraoxide (Co3O4) is extensively employed as a heterogeneous phase of Co for Oxone activation. Since Co3O4 can be manipulated to exhibit various shapes, 2-dimensional plate-like morphology of Co3O4 can offer large contact surfaces. If the large plate-like surfaces can be even porous, forming porous nanoplate Co3O4 (PNC), such a PNC should be a promising catalyst for Oxone activation. Therefore, a facile but straightforward method is proposed to prepare such a PNC for activating Oxone to degrade pollutants. In particular, a cobaltic coordination polymer with a morphology of hexagonal nanoplate, which is synthesized through coordination between Co2+ and thiocyanuric acid (TCA), is adopted as a precursor. Through calcination, CoTCA could be transformed into hexagonal nanoplate-like Co3O4 with pores to become PNC. This PNC also shows different characteristics from the commercial Co3O4 nanoparticle (NP) in terms of surficial reactivity and textural properties. Thus, PNC exhibits a much higher catalytic activity than the commercial Co3O4 NP towards activation of Oxone to degrade a model contaminant, salicylic acid (SA). Specifically, SA was 100% degraded by PNC activating Oxone within 120 min, and the Ea of SA degradation by PNC-activated Oxone is 70.2 kJ/mol. PNC can also remain stable and effective for SA degradation even in the presence of other anions, and PNC could be reused over multiple cycles without significant loss of catalytic activity. These features validate that PNC is a promising and useful Co-based catalyst for Oxone activation.
Production of multi-functional zinc oxide nanoparticles (ZnO-NPs) for wastewater treatment through green-approaches is a desirable alternative for conventional synthesis routes. Biomass waste valorization for nanoparticles synthesis has received increased research attention. The present study reports date pulp waste (DPW) utilization as an effective bio-reductant for green-synthesis of ZnO-NPs. A simple and eco-friendly process with low reaction time and calcination temperature was adopted for DPW mediated ZnO-NPs (DP-ZnO-NPs) synthesis. Microscopic investigations of DP-ZnO-NPs confirmed the non-agglomeration and spherical nature of particles with mean diameter of 30 nm. EDX and XPS analysis defined the chemical composition and product purity of DP-ZnO-NPs. UV and photoluminescence studies exhibited surface plasmonic resonance at 381 nm and fluorescent nature of DP-ZnO-NPs. FTIR studies established a formation mechanism outline for DP-ZnO-NPs. XRD and Raman investigations confirmed the crystalline and hexagonal wurtzite phase of DP-ZnO-NPs. DSC/TG analysis displayed the thermal stability of DP-ZnO-NPs with <10 wt% loss upto 700 °C. Photocatalytic degradation of hazardous methylene blue and eosin yellow dyes using DP-ZnO-NPs, showed rapid decomposition rate with 90 % degradation efficiency. Additionally, DP-ZnO-NPs demonstrated significant antibacterial effects on various pathogenic bacteria in terms of zone-of-inhibition measured by disc-diffusion method. Thus, the as-prepared DP-ZnO-NPs is suitable for industrial wastewater treatment.
The adsorption of residue oil from palm oil mill effluent (POME) using chitosan powder and flake has been investigated. POME contains about 2g/l of residue oil, which has to be treated efficiently before it can be discharged. Experiments were carried out as a function of different initial concentrations of residue oil, weight dosage, contact time and pH of chitosan in powder and flake form to obtain the optimum conditions for the adsorption of residue oil from POME. The powder form of chitosan exhibited a greater rate compared to the flake type. The results obtained showed that chitosan powder, at a dosage of 0.5g/l, 15min of contact time and a pH value of 5.0, presented the most suitable conditions for the adsorption of residue oil from POME. The adsorption process performed almost 99% of residue oil removal from POME. Equilibrium studies have been carried out to determine the capacity of chitosan for the adsorption of residue oil from POME using the optimum conditions from the flocculation at different initial concentrations of residue oil. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherms and isotherm constants. Equilibrium data fitted very well with the Freundlich model. The pseudo first- and second-order kinetic models and intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted well with the second-order kinetic model, which indicates that the chemical sorption is the rate-limiting step, i.e. chemisorption between residue oil and chitosan. The significant uptake of residue oil on chitosan was further proved by BET surface area analysis and SEM micrographs.
Today, a major issue about water pollution is the residual dyes from different sources (e.g., textile industries, paper and pulp industries, dye and dye intermediates industries, pharmaceutical industries, tannery and craft bleaching industries, etc.), and a wide variety of persistent organic pollutants have been introduced into our natural water resources or wastewater treatment systems. In fact, it is highly toxic and hazardous to the living organism; thus, the removal of these organic contaminants prior to discharge into the environment is essential. Varieties of techniques have been employed to degrade those organic contaminants and advanced heterogeneous photocatalysis involving zinc oxide (ZnO) photocatalyst appears to be one of the most promising technology. In recent years, ZnO photocatalyst have attracted much attention due to their extraordinary characteristics. The high efficiency of ZnO photocatalyst in heterogeneous photocatalysis reaction requires a suitable architecture that minimizes electron loss during excitation state and maximizes photon absorption. In order to further improve the immigration of photo-induced charge carriers during excitation state, considerable effort has to be exerted to further improve the heterogeneous photocatalysis under UV/visible/solar illumination. Lately, interesting and unique features of metal doping or binary oxide photocatalyst system have gained much attention and became favourite research matter among various groups of scientists. It was noted that the properties of this metal doping or binary oxide photocatalyst system primarily depend on the nature of the preparation method and the role of optimum dopants content incorporated into the ZnO photocatalyst. Therefore, this paper presents a critical review of recent achievements in the modification of ZnO photocatalyst for organic contaminants degradation.