Removal of trace organics by MBR treatment: the role of molecular properties

This study examined the relationship between specific molecular features of trace organic contaminants and their removal efficiencies by a laboratory scale membrane bioreactor (MBR). Removal efficiencies of 40 trace organic compounds were assessed under stable operating conditions. The reported results demonstrate an apparent correlation between chemical structures and the removal of trace organic contaminants by the laboratory scale MBR system. The removal of all 14 very hydrophobic (Log D \u3e 3.2) trace organic compounds selected in this study was consistently high and was above 85%. The occurrence and types of electron withdrawing or donating functional groups appear to be important factors governing their removal by MBR treatment. In this study, all hydrophilic and moderately hydrophobic (Log D \u3c 3.2) compounds possessing strong electron withdrawing functional groups showed removal efficiency of less than 20%. In contrast, high removal efficiencies were observed with most compounds bearing electron donating functional groups such as hydroxyl and primary amine groups. A qualitative framework for the assessment of trace organic removal by MBR treatment was proposed to provide further insights into the removal mechanisms

Removal of trace organics by MBR treatment: The role of molecular properties

This study examined the relationship between specific molecular features of trace organic contaminants and their removal efficiencies by a laboratory scale membrane bioreactor (MBR). Removal efficiencies of 40 trace organic compounds were assessed under stable operating conditions. The reported results demonstrate an apparent correlation between chemical structures and the removal of trace organic contaminants by the laboratory scale MBR system. The removal of all 14 very hydrophobic (Log D \u3e 3.2) trace organic compounds selected in this study was consistently high and was above 85%. The occurrence and types of electron withdrawing or donating functional groups appear to be important factors governing their removal by MBR treatment. In this study, all hydrophilic and moderately hydrophobic (Log D \u3c 3.2) compounds possessing strong electron withdrawing functional groups showed removal efficiency of less than 20%. In contrast, high removal efficiencies were observed with most compounds bearing electron donating functional groups such as hydroxyl and primary amine groups. A qualitative framework for the assessment of trace organic removal by MBR treatment was proposed to provide further insights into the removal mechanisms

Monitoring of seagrasses in Lake Illawarra, NSW

This research investigated the natural variability in leaf, shoot and meadow characteristics of Zostera capricorni in a coastal lagoon in SE Australia. The primary objective was to determine a set of parameters which may be indicative of the health of the major seagrass beds and which could be adopted in any long-term monitoring program. The study site was Lake Illawarra, a micro-tidal coastal lagoon located approximately 80 km south of Sydney (Australia), which contains approximately 5km2 of seagrass beds. A pilot study investigated the optimum quadrat size and sample size for measuring seagrass characteristics, given the natural variability of seagrasses in the Lake. It was found that 20 quadrats of 0.25 m2 could detect a change in seagrass percent cover of about 40% or more. The main study was carried out during winter and spring (2005) at three locations containing extensive seagrass beds, namely: Windang Peninsula; Bevans Island; and, Haywards Bay. At each location, sites were chosen at two depths, shallow (~ 1 m depth) and deep (~ 2m depth). Leaf, shoot and meadow parameters were assessed at each depth and location for each season. The measurements were designed to minimize damage to the seagrass beds. Leaf parameters assessed were number of leaves per shoot, maximum leaf length, leaf area per shoot, leaf mass, epiphyte mass and ratio of epiphyte to leaf mass. Percent cover was the major shoot parameter measured. Meadow condition was investigated by a relatively new technique involving small-scale strip mapping. Results indicated that maximum leaf length, leaf area, leaf mass, epiphyte mass and ratio of epiphyte to leaf mass displayed consistent patterns with significant differences between seasons and depths. Percent cover exhibited no consistent pattern between depths and seasons. The small-scale strip maps revealed differences in the degree and type of fragmentation of seagrass meadows between different sites. Overall, these studies suggested that leaf characteristics such as maximum leaf length, leaf area, epiphyte mass and ratio of epiphyte to leaf mass would be useful as indicators of the relative health of seagrass beds in Lake Illawarra. The small-scale mapping, which detected patterns in bed fragmentation, appeared to be an excellent early warning indicator of disturbance. As a result of this research, a protocol has been suggested for monitoring the seagrass meadows in Lake Illawarra

Removal of trace organic contaminants by membrane bioreactors (MBRs)

This research investigates the removal of trace organics by membrane bioreactors (MBRs) under various operating conditions to elucidate the removal mechanisms and factors affecting the removal efficiency of these contaminants. The reported results show excellent performance of a laboratory scale MBR system regarding the removal of basic biological performance with stable removal efficiency throughout over two years. Changes in operating conditions including mixed liquor pH, temperature, salinity could affect the performance of the MBR system at extreme conditions. However, the MBR system could quickly recover after returning to a normal operating condition. In contrast, mixed liquor suspended solid (MLSS) and dissolved oxygen (DO) concentration could not exert any discernible effects on the performance of the MBR. A set of 40 trace organics was selected to investigate the removal efficiencies and the associated removal mechanisms under a stable operating condition. The study demonstrated an obvious correlation between molecular features and the removal of trace organic contaminants by MBR system. The results revealed high removal efficiencies (\u3e85%) of very hydrophobic trace organic compounds (log D at pH 8 \u3e 3.2). Moreover, the occurrence of electron withdrawing or electron donating functional groups was found to be another important factor governing their removal. All hydrophilic and moderately hydrophobic (log D \u3c 3.2) compounds possessing only electron withdrawing functional groups consistently showed removal efficiency of well below 20%. In contrast, high removal efficiency was observed with most compounds bearing electron donating functional groups such as hydroxyl groups and carboxylic groups. The effect of mixed liquor pH (between pH 5 and 9) on removal of 10 selected trace organics was investigated. The results showed that ionisable trace organics (sulfamethoxazole, ibuprofen, ketoprofen and diclofenac) was strongly pH dependent. High removal efficiency of these compounds was observed at pH at 5 due to predominant hydrophobic form. This results in readily adsorb to sludge compared to basic condition. On the other hand, the removal efficiencies of bisphenol A and carbamazepine which are non-ionisable compounds were independent of the mixed liquor pH. The effect of operating conditions on the MBR performance regarding to removal of trace organic compound was determined. Four important operating conditions including hydraulic retention time (HRT), DO concentration, temperature and MLSS concentration were selected for this study. The results showed that higher HRTs had a large impact on the removal of compounds which were biodegradable whereas HRT could not influence the removal efficiency of high persistent biodegradable compounds and hydrophobic compounds. DO concentrations ranging 2 to 5 mg/L had no discernible influence on the removal of compounds exception for bisphenol A and estrone. Temperature had also no impact on the removal efficiency of model compounds exception for carbamazipine with 50% removal at higher temperature of 25°C. There was some fluctuation of removal efficiencies of compounds during MLSS experiment. The reported results were not conclusive to ascertain whether MLSS concentration would have any effects on the removal of trace organic compounds. This might be because of the unstable sludge retention time (SRT) in the MBR system. Change in salinity influent ranging of 1 to 12 g/L in MBR system appeared to exert a small effect on the removal of basic biological performance when exposed to higher salt concentration. The soluble microbial product (SMP) in form of protein increased resulting from disturbance in microbial behaviour. In contrast, with the exception of bisphenol A, no impact of salinity on removal of selected trace organic contaminants could be observed

Membrane bioreactor technology for decentralised wastewater treatment

Driven by stricter environmental regulations and legalisation on wastewater discharge and shrinking fresh water resources, water treatment has become an area of significant concern while at the same time there is a growing interest in utilising non-traditional water resources by means of water reclamation and water recycling

Removal of trace organic contaminants by submerged membrane bioreactors

Laboratory scale experiments were conducted to investigate the removal mechanisms of trace organic contaminants using a submerged MBR system. The system was equipped with a Zeenon ZW-1 membrane module. Bisphenol A (BPA) and sulfamethoxazole were selected as model trace organics for the EDCs and PhACs, respectively. Results obtained from this study demonstrate an excellent performance of MBRs regarding basic water quality parameters such as turbidity, TOC and TN. However, removal efficiency of specific trace organic contaminants was found strongly dependent on their physicochemical properties. Approximately 90% removal of BPA was recorded, while under the same condition, the removal efficiency of sulfamethoxazole was only about 50%. Both biodegradation and adsorption to the sludge were thought to be responsible for the removal of BPA, which is a relatively hydrophobic organic compound. In contrast, the latter mechanism was absent for sulfamethoxazole as this compound is rather hydrophilic. Results reported here indicate that it may be possible to predict the removal efficiency of trace organic contaminants by a submerged MBR system based on their physicochemical properties. This would lead to better selection of subsequent complementary treatment processes prior to indirect potable water reuse

Membrane bioreactor technology for decentralised wastewater treatment and reuse

There is a growing interest in utilising non-traditional water resources by means of water reclamation and water recycling for long term sustainability. Amongst the many treatment alternatives, membrane bioreactors (MBRs) have been seen as an effective technology capable of transforming various types of wastewater into high-quality effluent exceeding most discharge requirements and suitable for a variety of reuse applications. To date MBRs are largely restricted to centralised large scale applications, with the most common capacity of 200 ML per day or above. The aim of this paper is to review and discuss the potential and limitations of MBRs for small scale applications. Both technical and economic considerations will be delineated with respect to the future water outlook in Australia. Particular attention is also given to the impact of MBR technology on the removal of micropollutants that are of significant concern in water recycling

Strategies to enhance the removal of the persistent pharmaceutically active compound carbamazepine by membrane bioreactors

Carbamazepine, which is an anti-epileptic drug, is ubiquitously present in municipal wastewater. Owing to its recalcitrant chemical structure, carbamazepine is not significantly removed during conventional biological treatment or even by membrane bioreactor (MBR). With the ultimate aim of providing insights into the strategies to enhance carbamazepine removal, the effect of key operational parameters, namely, loading rate (2–750 μg/L• d), pH (5–9), mixed liquor suspended solids (MLSS) concentration (1–15 g/L) and dissolved oxygen (DO)