Characterising Treated Secondary Wastewater For Drinking Purposes Following Reverse Osmosis Treatment

Transcription

1 Characterising Treated Secondary Wastewater For Drinking Purposes Following Reverse Osmosis Treatment Palenque Blair(1), Kathryn L Linge(2), Francesco Busetti(2), Clemencia Rodriguez(3), Mark Handyside(1), Justin Blythe(4), Melissa Bromley(5), Oana Chirila(6), Simon Higginson(1), Anna Heitz(2), Cynthia Joll(2), Clare Newby(7), Simon Toze(8). 1-Water Corporation of Western Australia, Perth, WA, Australia, 2-Curtin Water Quality Research Centre, Perth, WA, Australia, 3-Department of Health, Perth, WA, Australia, 4-Kellogg Brown & Root Pty Ltd, Perth, WA, Australia, 5-Department of Water, Perth, WA, Australia, 6-National Measurement Institute, Perth, WA, Australia, 7-ChemCentre, Perth, WA, Australia, 8-CSIRO Land and Water, Brisbane, Qld, Australia palenque.blair@watercorporation.com.au, k.linge@curtin.edu.au Abstract No. 847 Introduction A key initiative for Western Australia is 30% reuse of treated wastewater by However, a lack of knowledge of health and environmental risks associated with micropollutants in wastewater has been a major barrier preventing establishment of large reuse schemes. In 2005 the Western Australian government awarded a grant to the Dept of Health, Dept of Environment, Water Corporation, Curtin University, Chemistry Centre of WA, CSIRO and the National Measurement Institute to complete a collaborative project on recycled water quality in the context of potential re-injection to groundwater. Now completed, this project has produced locally relevant information on micropollutants in wastewater to assess the safety of recycled water under Western Australian conditions, and micropollutant removal by micro-filtration (MF) and reverse osmosis (RO).

2 Objectives Characterise the microbial and chemical constituents in secondary treated wastewater from the three major wastewater treatment plants (WWTPs) in Perth, Western Australia Assess the performance of micro-filtration and reverse osmosis (MF/RO) treatment to produce water of the required standard for augmentation of drinking water supplies by re-injection into groundwater Use the research results to develop and refine health and environmental guidelines Chemicals! 396 chemicals, in 15 different chemical classes (see Table)! Selected based upon! current use in Western Australia! toxicological concern! prior detection in wastewater as reported in scientific literature! Eight laboratories involved in analysis!!"#$%&'()!")(** O"-%&.'%#9,"-%&&249. *".:749". J%&25"#%-"9'CH*.!FM4-$2.%,4#". +,%-$.!/0 12()34$* >N??I => B!!"#$%&'()!")(** *0%$,%7"<:7%&. ;#42#. 8%94%:2# 6.-$25"#47 02$,2#". +,%-$.!/0 12()34$* =A = Number of analytes measured in each chemical class! More than 20,000 records excluding field and trip blanks L/1. *;J. KI?I 12,+&"34#5'%5"#-. Microbiological and effluent toxicity tests also undertaken C4234#D'E<$%#.'%# #F&4G"'*1H. *0"#2&. >B?A!"#"$%&'(()* +%$%,"-"$. =>

3 Sampling! Three metropolitan WWTPs! Beenyup (north), Subiaco (central/city) and Woodman Point (south/industry)! Currently discharge to ocean! Kwinana Water Reclamation Plant (KWRP)! MF/RO plant producing tertiary treated water for industry (~17 ML/day) Beenyup WWTP and BPP Subiaco WWTP Map showing location of sampling sites. Images courtesy of Google Maps! Beenyup Pilot Plant (BPP)! MF/RO Plant (~ 0.1 ML/ day) commissioned at Beenyup WWTP in September 2007 for the project Composite samples were taken using an automated ISCO 4700 refrigerated sampler over 24h Woodman Point WWTP KWRP Perth, Western Australia! Grab or composite (see photo left) samples collected depending on the analyte! Seven sampling events over 2 years (Event 7 for N-nitrosamines only)! Preliminary sampling event conducted in June 2005 at KWRP! Raw groundwater (drinking water source) monitored on the influent to the Wanneroo Groundwater Treatment Plant

4 Health Risk Assessment Health values are concentrations considered safe for lifetime consumption and were calculated using the three-tiered approach recommended in the Australian Guidelines for Water Recycling (2008). For chemicals without existing guidelines or toxicological information, the very conservative Threshold of Toxicological Concern (TTC) approach was used to derive the health value. A Risk Quotient (RQ) was calculated as the ratio between the measured concentration of the chemical and the health value. RQ < 1 implies low health risk RQ(max) used maximum concentration measured for each analyte, RQ(median) used median concentration, with all nondetects (reported as the LOD) If a chemical was never detected RQ(median) was calculated based on the median LOD Erythromycin-H2O metronidazole sulfamethoxazole NDMA NDBA NDPA NDEA Health Value (ug/l) Source Pharmacoepia Pharmacoepia Pharmacoepia AGWR IRIS Cal DPH AGWR Secondary WW RQ(med) RQ(max) Post-RO Water RQ(med) RQ(max) na na na Example RQ values for selected antibiotics (orange), N-nitrosamines (blue), and halogenated DBPs (green). The impact of using the TTC to calculate health values is illustrated by the significant difference in RQ calculated for the DBPs. While N- nitrosamines post-ro RQ(max) >1, potential public health impact is considered low (see conclusions) NEMA NPIP NMOR NPYR Bromoform Chloroform Bromodichloroacetaldehyde IRIS OEHHA OEHHA IRIS WHO AGWR TTC n/a Dibromoacetaldehyde 0.7 TTC 0.3 n/a

5 Results! Of the 396 compounds analysed, 195 were detected at least once in secondary WW. In post-ro water, 140 were detected at least once! Generally there were no real differences between WWTPs or variation with season Eight compounds had higher percentage detection in post-ro than in secondary wastewater, and this was attributed to contamination (e.g. toluene) formation during chloramination (e.g. halomethanes, see Figure below) unintentional addition during the MF/RO process (e.g. acrylonitrile, chlorate) Demonstrates that the chloramination procedure, membrane materials and anti-scalant chemicals usage need to also be considered as potential sources of chemicals in post-ro water. Calculation of treatment efficiency is significantly affected by sample location (see Figure below). For chemicals that form or are added during treatment, calculations across the whole treatment train do not reflect RO removal efficiency. RO treatment performance requires monitoring immediately prior to RO rather than using secondary wastewater, particularly for all DBPs. Microbiological Analysis Microbiological characterisation of secondary WW indicated that thermotolerant coliforms and enterococci were always detectable. Virus challenge tests in BPP using the coliphage MS2 as a surrogate of enteric virus demonstrate that RO alone was able to achieve at least 4 log removal of virus particles Schematic showing MF/RO treatment process, including prechloramination to protect the RO membrane. Overall treatment efficiency can be determined by comparing Wastewater and Post- RO samples, but RO treatment efficiency should compare Post-MF and Post-RO samples

6 Most Frequently Detected Compounds in post-ro water! 12 out of 396 compounds were found in > 50% detection in post-ro! Most frequently detected were! Disinfection by-products possibly affected by chloramination! Metals present in high concentrations in secondary wastewater! Chemicals attributed to release from MF or RO membranes themselves

7 Indicator Compounds! How can water quality and treatment performance be monitored without measuring every chemical?! An indicator is chemical or microbial parameter that can be used to measure the effectiveness of a process (AGWR, 2008).! A key outcome of this research was the identification of chemical indicators of RO treatment performance and recycled water quality indicators relevant for Western Australia.! These indicators have been recommended for use in the Water Corporation of Western Australia s Groundwater Replenishment Trial (GWRT)!. Treatment Performance Indicators! Have chemical or physical characteristics that can be linked to the removal mechanism! Are present in wastewater at sufficiently high concentrations with sufficient frequency (typically >80% detection) to determine the degree of reduction through a process! Key properties for chemical rejection by MF/RO! size (molecular weight, width and length)! hydrophobicity (log Kow, log D)! polarity (dipole moment)! acidic/basic character (pka)! solubility in water (associated with chemical charge). Recycled Water Quality Indicators! Demonstrate safety of the MF/RO treated water with respect to a group of compounds that share similar physical and chemical properties.! Provide additional confidence beyond treatment performance monitoring! Useful particularly for chemical classes where no chemical was detected in wastewater with sufficient concentration or frequency to be used as a Treatment Performance Indicator

8 Chemicals selected to be indicators of RO Treatment Performance and Recycled Water Quality. Molecular weight classification: Small <150 g/mol; Medium g/mol; Large >250 g/mol

9 Conclusions! MF/RO reliably produces recycled water suitable for augmenting public drinking water supplies.! N-nitrosamines were the only chemical group identified as a potential health concern (particularly NDMA).! NDMA was routinely detected, occasionally above the AGWR value of 10 ng/l after the MF/RO treatment, although average and median NDMA concentrations complied with the AGWR guideline! The DRAFT - Revised Australian Drinking Water Guidelines (2010) recommend a health value of 100 ng/l, as per the WHO (2006) and this was never exceeded. It is considered that the derivation of the one in a million cancer risk would impose a disproportionate regulatory burden on water suppliers while having little impact on total population exposures.! MF/RO plant optimisation or precursor removal may reduce post-ro N-nitrosamine concentrations! The project provided the information necessary for health and environmental recommendations to be developed for the Groundwater Replenishment Trial (GWRT).! Key chemicals (indicators of treatment performance and recycled water quality) were identified for monitoring during the GWRT.! This research indicates that there will be a high degree of safety associated with further investigation of indirect potable reuse in Western Australia that uses MF/RO treatment in the treatment train, providing confidence to proceed with the GWRT. Further information is available in the full technical report: Premier's Collaborative Research Program ( ): "Characterising Treated Wastewater For Drinking Purposes Following Reverse Osmosis Treatment". Technical Report, Published by Department of Health, Western Australia ISBN Acknowledgements This project was funded by the Premier s Collaborative Research Program (PCRP), collaborative science program designed to encourage a range of Western Australian researchers to pool their knowledge and expertise. Collaborating organisations included government (Department of Health, Department of Environment, and Department of Water), research (CSIRO, Curtin Water Quality Research Centre) and industry (National Measurement Institute, Chemistry Centre of WA, and the Water Corporation of Western Australia).