Imperative assessment on the current status of rubber wastewater treatment: Research development and future perspectives.

The environment has been significantly impacted by the rubber industry through the release of large quantities of wastewater during various industrial processes. Therefore, it is crucial to treat the wastewater from the rubber industry before discharging it into natural water bodies. With the understanding that alarmingly depleting freshwater sources need to be preserved for future generations, this paper reviews the status of the rubber industry and the pollution caused by them, focusing mainly on water pollution. The review pays special attention to the recent advancements in wastewater treatment techniques for rubber industry wastewater categorizing them into pre-treatment, secondary, and tertiary treatment processes while discussing the advantages and disadvantages. Through a comprehensive analysis of existing literature, it was determined that organic content and NH4+ are the most frequently focused water quality parameters, and despite some treatment methods demonstrating superior performance, many of the methods still face limitations and require further research to improve systems to handle high organic loading on the treatment systems and to implement them in industrial scale. The paper also explores the potential of utilizing untreated or treated wastewater and byproducts of wastewater treatment in contributing towards achieving several United Nations sustainable development goals (UN-SDGs); SDG 6, SDG 7, SDG 9, and SDG 12.

Post-treatment of matured landfill leachate: Synthesis and evaluation of chitosan biomaterial based derivatives as adsorbents.

Matured landfill leachate is complex in nature, hence, a single conventional treatment unit is insufficient to remove the contaminants of the leachate to achieve the discharge standards. Furthermore, high levels of organic matter, colour compounds, and iron-based materials form a dark black/brown colour in leachate which is not removed by the biological treatment units. Hence, an Anoxic-Oxic Membrane Bioreactor coupled with a tertiary adsorption unit composed of crosslinked-protonated chitosan was tested for effective removal of the colour of the permeate. Several operational parameters such a pH, contact time, and adsorbent dosage on the adsorptive removal of colour were quantified using sorption-desorption experiments. Furthermore, the biosorbent was characterized using FTIR, SEM, XRD, BET-specific surface area, and pHZPC. Response Surface analysis confirmed the optimization of operational parameters conducted through traditional batch experiments. Langmuir isotherm model fitted with equilibrium data (R2 = 0.979) indicating a monolayer homogeneous adsorption. Kinetic data followed the Pseudo-Second-Order model (R2 = 0.9861), showing that the adsorbent material has abundant active sites. The percentage removal values show that the colour removal increases with time of contact and dosage of adsorbent, but removal is mainly influenced by the solution pH levels. The experimental results manifested a colour removal efficiency of 96 ± 3.8% obtained at optimum conditions (pH = 2, adsorbent dosage = 20 g/L, contact time = 48 h) along with an adsorption capacity of 123.8 Pt-Co/g suggesting that the studied adsorbent can be used as an environmentally friendly biosorbent in a tertiary unit for colour removal in a treatment system which is used to treat matured landfill leachate.

Treatment of mature landfill leachate in tropical climate using membrane bioreactors with different configurations.

This study describes the collection of landfill leachate from seven sites in different climatic zones of Sri Lanka and characterizes the landfills through the analyses of leachate quality. Membrane bioreactors (MBRs) with different configurations were employed to treat some of those leachates. An aerobic MBR (AMBR) system was operated in three Phases. In the first Phase, an AMBR alone, in the second Phase an anaerobic reactor followed by an anoxic reactor and an AMBR and in the third Phase an anoxic reactor followed by an AMBR were operated. In Phases I and II, the sludge retention time (SRT) and the hydraulic retention time (HRT) were kept at infinite (as no intentional wasting of sludge was made) and 96 h; in Phase III, the SRT was varied from 60, 30, 20 to 10 days and under each SRT, the HRT was varied from 96, 48, 24 and 12 h. The optimum operating conditions for the configuration used in Phase III was established through extensive experiments which had a SRT. The three MBR configurations removed more than 93%, 64.8% and 59% of BOD5, COD and total nitrogen respectively. They also removed large amounts of slowly biodegradable substances and nitrogenous compounds other than NH4+, NO3- and NO2-. Relationships between SRT and MLSS as well as SRT and fouling rate of membrane have been found. The study illustrates the capabilities of MBR in treating landfill leachate.

Integrated mathematical model to simulate the performance of a membrane bioreactor.

Membrane bioreactor technology includes the integration of biological wastewater treatment and physical separation by membrane filtration. When analyzing the system performance, efficiency of biological processes, physical separation and membrane fouling must be taken into consideration. Over the years, mathematical modelling of wastewater treatment has evolved and is being used extensively to optimize the performance of treatment systems. A Number of attempts have been made towards the development of mathematical models for membrane bioreactors and most of these models have not considered the effect of soluble microbial products on membrane fouling. Also the effect of periodic membrane cleaning was neglected. In this study, an integrated mathematical model was developed for the membrane bioreactor. A biological model based on activated sludge processes (extended with biopolymer kinetics) and a physical model with cake layer kinetics and membrane fouling have been combined. In order to overcome the drawbacks of previous attempts of modelling, the influence of soluble microbial products and extracellular polymeric substances are considered in the model integration. Further, the physical processes of the sludge removal and membrane cleaning which have strong influence on membrane fouling are considered in the model. "AQUASIM", a computer program for the identification and simulation of aquatic systems, was used for solving the processes. Calibrated and validated model enables the prediction of the system performance and membrane fouling under different operating conditions.

Influence of pyrolysis parameters on phosphorus fractions of biosolids derived biochar.

Transforming biosolids into biochar, through pyrolysis, could result in more sustainable waste management. Influence of pyrolysis conditions (temperature, heating rate and residence time) on physico-chemical properties of biosolids (collected at Mount Martha Water Recycling Plant, Melbourne), phosphorus fractions and phosphorus forms was investigated. Twelve different biochar samples were produced at 400, 500 and 600 °C, at two heating rates (5 and 20 °C/min) and at two residence times (30 and 120 min). Biochar yield, pH, electrical conductivity (EC), elements (C, H and N) and BET surface area were analysed. Sequential extraction of P in biosolids and resultant biochars was done using Hedley method. Characterization was completed with SEM images and results from 31P liquid state NMR. Increased temperatures would not only increase the alkalinity, decrease EC and increase the adsorption capacity by increasing the surface area but also convert the readily available P to a less available pool. Therefore, this nutrient might be released to soil slowly over a longer period of time. The results showed that temperature, along with residence time and heating rate, had a significant effect on the characteristics observed. Therefore, all these factors need to be carefully considered when preparing biochar for use as a soil amendment.

Computing the effective diffusion coefficient of solutes in a multi-salts solutions during forward osmosis (FO) membrane filtration: Experiments and mathematical modelling.

Diffusion coefficient of solutes through a porous membrane media is different from diffusion coefficient through a free homogenous media. Porosity, tortuosity and the thickness of the membrane significantly affect the diffusion through a specific thickness of a membrane and therefore it is termed as effective diffusion coefficient (Deff) which is lower than the actual diffusion coefficient, D. The Deff of single or dual solutes through a porous membrane layer are well documented but not for multiple salts. Therefore, in this study, single, dual and multiple salt mixtures were passed through a flat sheet cellulose triacetate Forward Osmosis (FO) membrane to obtain a semi-empirical relationship with the Deff and its water flux. This will allow computing the structural coefficient of FO membranes. Research community have spent tremendous efforts in membrane modification to reduce the structural coefficient to improve FO process efficiency. Our finding suggests that optimising the draw solution chemistry can achieve this goal.

Treatment of ametryn in wastewater by a hybrid MBR system: a lab-scale study.

Agricultural discharge of herbicides to the Great Barrier Reef (GBR) poses significant threat to the marine ecosystem. This study evaluates the performance of a hybrid treatment system consists of a membrane bioreactor (MBR), UV disinfection unit and a granular activated carbon (GAC) column in treating ametryn which is one of the major herbicides in agricultural discharges. While the MBR alone removes only 40% of ametryn at a hydraulic retention time of 7.8 h, the hybrid system removed ametryn to below detection levels.

Influence of biofilm carriers on membrane fouling propensity in moving biofilm membrane bioreactor.

In moving biofilm membrane bioreactor (MB-MBR) sponge carriers for biofilm growth were coupled with conventional submerged membrane bioreactor (C-MBR). This study compared the fouling propensity of C-MBR with MB-MBR and investigated factors affecting fouling variations in both the systems. Membrane fouling tendencies were monitored in terms of trans-membrane pressure (TMP) and the fouling characterization included membrane fouling resistances in situ and specific cake resistance (SCR) in batch filtration cell. Comparison of TMP profiles depicted prolong filtration periods in MB-MBR. Cake layer resistance (R(c)), pore blocking resistance (R(p)) as well as SCR were higher in C-MBR. The study reveals that hybrid biomass in MB-MBR creates relatively more porous cake structure in the absence of filamentous bacteria which were found in abundance in C-MBR. Filamentous bacteria were also responsible for the release of high concentration of carbohydrates in the form of soluble extra polymeric substance (EPS) contributing to higher R(p) in C-MBR.

Effect of powdered activated carbon (PAC) and cationic polymer on biofouling mitigation in hybrid MBRs.

In this study, the influence of powdered activated carbon (PAC) and cationic polymer (MPE50) was investigated on the fouling propensity in hybrid MBRs. Three laboratory scale MBRs were operated simultaneously including MBR(Control), MBR(PAC), and MBR(Polymer). Optimum dosages of PAC and polymer to the MBR(PAC) and MBR(Polymer), respectively were determined using jar tests. It was found that the MBR(PAC) exhibited low fouling tendency and prolonged filtration as compared to the other MBRs. Improved filtration in MBR(PAC) was attributed to the flocculation and adsorption phenomena. The effective stability of the biomass by PAC in the form of biological activated carbon (BAC) was verified by the increase in mean particle size. The BAC aided sludge layer exhibited porous cake structure resulting in the prolong filtration. However, both the membrane hybrid systems revealed effective adsorption of organic matter by 40% reduction in the soluble EPS concentration.

Assessments of critical flux in a pilot-scale membrane bioreactor.

In this study, the influence of various parameters such as determination methods and step height and length of incremental flux on critical flux values were investigated. Experiments were carried out on a pilot-scale membrane bioreactor (MBR) treated municipal wastewater. Three of the five critical flux determination methods, such as flux linearity, 90% permeability and flux cycling conducted in this study, indicated a decline in critical flux values as the step height of incremental flux increased. However, the hysteresis method and the two-third (2/3) flux limitation method showed an increase and independence of critical flux to the step height of incremental flux, respectively. On the other hand, the step length of incremental flux had no obvious effect on critical flux values evaluated by all critical flux determination methods. Like critical flux, sustainable flux has negative relationship with the increase of step height but no influence of step length was found in this study.

Performance of suspended and attached growth MBR systems in treating high strength synthetic wastewater.

The performance of laboratory-scale attached growth (AG) and suspended growth (SG) membrane bioreactors (MBRs) was evaluated in treating synthetic wastewater simulating high strength domestic wastewater. This study investigated the influence of sponge suspended carriers in AG-MBR system, occupying 15% reactor volume, on the removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), and compared it to that of SG-MBR. Results showed that the removal efficiencies of COD, TN and TP in AG-MBR were 98%, 89% and 58%, respectively as compared to 98%, 74% and 38%, respectively in SG-MBR. Improved TN removal in AG-MBR systems was primarily based on simultaneous nitrification and denitrification (SND) process. These results infer that the presence of small bio-particles having higher microbial activity and the growth of complex biomass captured within the suspended sponge carriers resulted in improved TN and TP removal in AG-MBR.

Prediction of membrane fouling in MBR systems using empirically estimated specific cake resistance.

The focus of this study was to empirically estimate the specific cake resistance (SCR) by the variation in shear intensity (G) in four laboratory-scale MBRs. The control reactor (MBR(0)) was operated with aeration only while other MBRs (MBR(150), MBR(300) and MBR(450)) were operated with aeration and mechanical mixing intensities of 150, 300 and 450 rpm, respectively. It was found that the SCR was strongly correlated (R(2)=0.99) with the fouling rates in the MBRs. Moreover, the contribution of cake resistance (R(c)) to the total hydraulic resistance (R(t)) was predominant compared to the irreversible fouling resistance (R(f)). On this basis, the cake filtration model was selected as a predictive tool for membrane fouling. This model was modified by replacing the SCR with its empirical shear intensity relationship. The modified model can predict the fouling rate for a given shear intensity (G) within 80 and 250 s(-1) in a MBR system.

Hydrogenotrophic denitrification of highly saline aquaculture wastewater using hollow fiber membrane bioreactor.

A hydrogenotrophic denitrification system with a hollow fiber membrane was evaluated for treating and recycling synthetic aquaculture wastewater. Hollow fibers ensured bubble-less diffusion of hydrogen and subsequent removal of nitrate from the first bioreactor. The second aerobic reactor was used for biomass filtration and removal of organic matter. Nitrate and organic matter expressed as dissolved organic carbon were 50 mgl(-1) and 20 mgl(-1), respectively, in the inlet. Acclimatization of hydrogenotrophic bacteria to 10, 20 and 30 ppt of salinity was also observed. Optimum hydraulic retention time and denitrification rate corresponding to these salinities were 3, 5 and 6 h and 366.8, 226.2 and 193.2 gm(-3) day(-1), respectively.

Mechanical mode floating medium filters for recirculating systems in aquaculture for higher solids retention and lower freshwater usage.

The aim of this work was to develop a better understanding of a floating medium in a mechanical filtration mode. The experiments were carried out using a commonly available polystyrene floating medium filter with the grain size of 1mm. A sand medium filter with the similar grain size was also tested for the comparison. A short-term trial of 2h and a long-term of 20 days filtration times were conducted with three custom manufactured pressurized filters of 16l. The filters were operated under three different configurations: (i) upflow with floating media (UFMF), (ii) downflow with floating media (DFMF) and (iii) downflow with a sand medium (DSF). The results of the long-term trial indicated that at a flow rate of 22 m/h, the UFMF and DSF had similar solid removal capacity with an average total suspended solids (TSS) removal efficiency of 60%. The DFMF could only remove 33% of TSS. However, during the short-term trial, TSS removal efficiency of the UFMF was better compared to the DSF (e.g., 71%, 56% and 57% of TSS removal in UFMF compared to 66%, 49% and 41% in the DSFF at the flow rates of 20, 25 and 31m/h, respectively). The energy requirements of each filter were compared by measuring the pressure differential across each filter. The long-term trial indicated that the UFMF had a significantly less pressure differential (44 kPa) compared to the DSF (80 kPa) (p<0.001). This was further confirmed that at different flow rates whereby the DSF displayed higher pressure differentials for filtration rates at 350, 450, 550 and 800 l/h. The study indicated that floating medium filter was better and more applicable to recirculating aquaculture systems than conventional pressurized sand filter.

An economic evaluation of phosphorus recovery as struvite from digester supernatant.

Phosphorus can be recovered from wastewater through crystallisation of struvite, MgNH(4)PO(4).6H(2)O. Approximately 1 kg of struvite can be crystallised from 100 m(3) of wastewater. Crystallisation is profitable compared to chemical and biological removal of phosphorus due to savings from the reduction in (i) chemicals used for precipitation and sludge disposal; and (ii) downtime for cleaning unwanted struvite formed during chemical and biological removal. The struvite produced annually from a wastewater treatment plant that processed 100 m3/d, would be sufficient to apply on 2.6 ha of arable land, as fertilizer. If struvite were to be recovered from wastewater treatment plants worldwide, 0.63 million tons of phosphorus (as P(2)O(5)) could be harvested annually, reducing phosphate rock mining by 1.6%. Therefore, this technology could provide opportunities to recover phosphorus sustainably from waste streams and preserve phosphorus reserves.

Granular activated carbon (GAC) adsorption in tertiary wastewater treatment: experiments and models.

Wastewater treatment has always been a major concern in the developed countries. Over the last few decades, activated carbon adsorption has gained importance as an alternative tertiary wastewater treatment and purification process. In this study, granular activated carbon (GAC) adsorption was evaluated in terms of total organic carbon (TOC) removal from low strength synthetic wastewater. This paper provides details on adsorption experiments conducted on synthetic wastewater to develop suitable adsorption isotherms. Although the inorganics used in the synthetic wastewater solution had an overall unfavourable effect on adsorption of organics, the GAC adsorption system was found to be effective in removing TOC from the wastewater. This study showed that equation of state (EOS) theory was able to fit the adsorption isotherm results more precisely than the most commonly used Freundlich isotherm. Biodegradation of the organics with time was the most crucial and important aspect of the system and it was taken into account in determining the isotherm parameters. Initial organic concentration of the wastewater was the determining factor of the model parameters, and hence the isotherm parameters were determined covering a wide range of initial organic concentrations of the wastewater. As such, the isotherm parameters derived using the EOS theory could predict the batch adsorption and fixed bed adsorption results of the multi-component system successfully. The isotherm parameters showed a significant effect on the determination of the mass transfer coefficients in batch and fixed bed systems.