Rejection of disinfection by-products by RO and NF membranes: influence of solute properties and operational parameters

The objective of this study was to determine the influence of solute properties and operational parameters on disinfection by-product (DBP) rejection by reverse osmosis (RO) and nanofiltration (NF) membranes. This was achieved by assessing the removal efficiency for 29 DBPs likely to be formed during disinfection of secondary effluents. The DBPs investigated were trihalomethanes, iodinated-trihalomethanes, haloacetonitriles, chloral hydrate, haloketones, halonitromethanes and haloacetamides.The performance of a NF and a low pressure RO membrane was investigated within a range of different pHs, temperatures, transmembrane fluxes, crossflow velocities and ionic strengths. Rejection decreased significantly with increasing temperature and decreasing transmembrane flux, while the influence of the other operational parameters was minimal with a few exceptions detailed in the manuscript.Multiple linear regression was used to determine the physico-chemical solute properties contributing significantly to DBP rejection. For NF, geometric parameters were revealed to be the dominant molecular descriptors influencing rejection, whereas for RO, besides size exclusion, solute-membrane interaction played an important role. A predictive model based on multiple linear regression was established that could forecast rejection of DBPs as a function of membrane operation parameters and DBP properties

Simulation and optimisation of a two-stage/two-pass reverse osmosis system for improved removal of chlorophenol from wastewater

YesReverse osmosis (RO) has become a common method for treating wastewater and removing several harmful organic compounds because of its relative ease of use and reduced costs. Chlorophenol is a toxic compound for humans and can readily be found in the wastewater of a wide range of industries. Previous research in this area of work has already provided promising results in respect of the performance of an individual spiral wound RO process for removing chlorophenol from wastewater, but the associated removal rates have stayed stubbornly low. The literature has so far confirmed that the efficiency of eliminating chlorophenol from wastewater using a pilot-scale of an individual spiral wound RO process is around 83 %, compared to 97 % for dimethylphenol. This paper explores the potential of an alternative configuration of two-stage/two-pass RO process for improving such low chlorophenol rejection rates via simulation and optimisation. The operational optimisation carried out is enhanced by constraining the total recovery rate to a realistic value by varying the system operating parameters according to the allowable limits of the process. The results indicate that the proposed configuration has the potential to increase the rejection of chlorophenol by 12.4 % while achieving 40 % total water recovery at an energy consumption of 1.949 kWh/m³

Effective removal of MIB and geosmin using MBBR for drinking water treatment

Biodegradation is an effective method for the removal of taste and odour (T&O) compounds from drinking water sources. In this study, the applicability of a moving-bed biofilm reactor (MBBR) as biological treatment step for the control of MIB and geosmin was studied at pilot-scale. After a 3.5 month acclimation period both T&O compounds could be reliably removed by at least 80%. Biodegradation was found to be the dominant removal mechanism with air stripping contributing up to 25% at shorter HRTs. Also sorption of MIB and geosmin onto carriers and biofilm did occur, simultaneously facilitating the biodegradation process. The biodegradation of MIB and geosmin followed pseudo-first-order kinetics

Factors affecting the formation of disinfection by-products during chlorination and chloramination of secondary effluent for the production of high quality recycled water

During the production of high quality recycled water by reverse osmosis membrane filtration secondary effluent must be disinfected to limit biofouling on the membrane surface. Advanced Water Treatment Plants in South East Queensland, Australia use disinfectant contact times ranging from 30min up to 24h. Disinfectants such as chlorine and chloramines react with effluent organic matter to generate disinfection by-products (DBPs) which could be potentially hazardous to human health if the water is destined for supplementing public water supplies. In this context, secondary effluents are of concern because of their high total organic carbon content which can act as DBP precursors. Also, effluent organic matter may form different DBPs to those formed from natural organic matter during conventional drinking water treatment, either in quantity, identity or simply in the abundance of different DBPs relative to each other. It cannot be assumed per se with certainty that DBP formation will be affected in the same way by operational changes as in drinking water production. Response surface modelling has been employed in this study at the bench scale to investigate the effect of reaction time (0-24h), pH (5.5-8.5), temperature (23-35°C), disinfection strategy (chlorine vs chloramines used prior to membrane treatment) and the interaction between these different parameters on DBP formation during disinfection of secondary effluent. The concentration of halogenated DBPs formed during the first 24h of reaction with the different disinfectants followed the order chlorination ≫ in line-formed monochloramine > pre-formed monochloramine. Contact time with chlorine was the major influencing factor on DBP formation during chlorination, except for the bromine-containing trihalomethanes and dibromoacetonitrile for which pH was more significant. Chlorination at high pH led to an increased formation of chloral hydrate, trichloronitromethane, dibromoacetonitrile and the four trihalomethanes while the opposite effect was observed for the other targeted DBPs. Temperature was identified as the least influencing parameter compared to pH and reaction time for all DBPs in all the disinfection strategies, except for the formation of chloral hydrate where pH and temperature had a similar significance and bromoform that was similarly affected by temperature and reaction time. Chloramines employed at pH 8.5 reduced the concentration of all studied DBPs compared to pH 5.5. Furthermore, reaction time was the most significant factor for trichloronitromethane, chloroform, trichloroacetonitrile, dichloroacetonitrile and bromochloroacetonitrile formation while pH was the most influencing factor affecting the formation of the remaining DBPs

Removal of Pharmaceuticals and Illicit Drugs from Wastewater Due to Ferric Dosing in Sewers

Ferric (Fe3+) salt dosing is an efficient sulfide control strategy in the sewer network, with potential for multiple benefits including phosphorus removal in the biological reactors and sulfide emission control in the anaerobic digesters of wastewater treatment plant (WWTP). This paper extends the knowledge on the benefit of iron dosing by exploring its impact on the fate of organic micropollutants (MPs) in the wastewater using sewer reactors simulating a rising main sewer pipe. The sulfide produced by the sewer biofilms reacted with Fe3+ forming black colored iron sulfide (FeS). Among the selected MPs, morphine, methadone, and atenolol had \u3e90% initial rapid removal within 5 min of ferric dosing in the sewer reactor. The ultimate removal after 6 h of retention time in the reactor reached 93-97%. Other compounds, ketamine, codeine, carbamazepine, and acesulfame had 30-70% concentration decrease. The ultimate removal varied between 35 and 70% depending on the biodegradability of those MPs. In contrast, paracetamol had no initial removal. The rapid removal of MPs was likely due to adsorption to the FeS surface, which is further confirmed by batch tests with different FeS concentrations. The results showed a direct relationship between the removal of MPs and FeS concentration. The transformation kinetics of these compounds in the reactor without Fe3+ dosing is in good agreement with biodegradation associated with the sewer biofilms in the reactor. This study revealed a significant additional benefit of dosing ferric salts in sewers, that is, the removal of MPs before the sewage enters the WWTP

Understanding the operational parameters affecting NDMA formation at Advanced Water Treatment Plants

N-nitrosodimethylamine (NDMA) can be formed when secondary effluents are disinfected by chloramines. By means of bench scale experiments this paper investigates operational parameters than can help Advanced Water Treatment Plants (AWTPs) to reduce the formation of NDMA during the production of high quality recycled water. The formation of NDMA was monitored during a contact time of 24 h using dimethylamine as NDMA model precursor and secondary effluent from wastewater treatment plants. The three chloramine disinfection strategies tested were pre-formed and in-line formed monochloramine, and pre-formed dichloramine. Although the latter is not employed on purpose in full-scale applications, it has been suggested as the main contributing chemical generating NDMA during chloramination. After 24 h, the NDMA formation decreased in both matrices tested in the order: pre-formed dichloramine > in-line formed monochloramine >> pre-formed monochloramine. The most important parameter to consider for the inhibition of NDMA formation was the length of contact time between disinfectant and wastewater. Formation of NDMA was initially inhibited for up to 6h with concentrations consistentl

Disinfection by-products management in high quality recycled water

During the production of high quality recycled water (HQRW) by means of reverse osmosis (RO) membrane filtration, chloramines (used to avoid biofouling) can generate disinfection by-products (DBPs) which could ultimately end up in the product water. This paper compares the fate of DBPs and organic halogen content generated during the production of HQRW under two different disinfection strategies employed prior to RO filtration: (i) in line-formed chloramines with a short contact time between secondary effluent and disinfectant versus (ii) pre-formed chloramines with a long contact time between secondary effluent and disinfectant. In general, pre-formed chloramines formed less trihalomethanes (THMs) in comparison to in line-formed chloramines even after a longer contact time. However, pre-formed chloramines still generated iodo-THMs (I-THMs) which are of concern since they are suspected to be more toxic than their chlorinated and brominated analogues. I-THMs were very effectively reduced by the advanced oxidation process placed after the membrane process. Chloramines also form other halogenated by-products whose identity is unknown. In this study, more than 95% of total organic halogen formed by chloramines was rejected by the RO membranes although the reduction of targeted low molecular weight DBPs was only around 50%. Specific rejections for individual DBPs vary, ranging from low for haloacetonitriles and high for haloketones

How to minimize disinfection by-products during the production of high quality recycled water

Advanced Water Treatment Plants (AWTPs) produce high quality recycled water (HQRW) treating secondary treated wastewater by means of coagulation, microfiltration, reverse osmosis filtration, advanced oxidation and final disinfection with chlorine. Chloramines are used prior to the membrane filtration to keep biofouling on the surface of the reverse osmosis membranes manageable. When organic and inorganic substances in water react with disinfectants such as chloramines, disinfection by-products (DBPs), which can be of concern due to their potential adverse effects on human health, are formed. This paper investigates the formation of DBPs during HQRW production at two full scale AWTPs and at bench scale. Concentrations measured in the chloraminated reverse osmosis feed water during the sampling campaigns at full scale were generally low, with individual DBP concentrations not greater than 3 μg/L. However, haloacetonitriles (HANs) were measured at levels close to the Queensland (Australia) regulation for water recycling. During bench scale experiments, formation of all DBPs measured proved to increase with contact time except haloketones which showed a rapid initial formation in the first half an hour, followed by a much slower rate of formation. The rejection behaviour of different DBPs by reverse osmosis membranes at full scale varied depending on the DBP intrinsic properties. For example, bulky molecules were well rejected while polar compounds, such as the HANs, showed a poorer rejection. Besides size exclusion, solute-membrane interactions play an important role in determining the extent of DBP removal. 201