The Combined Effects of Galvanic Interaction and Silicate Addition on the Oxidative Dissolution of Pyrite: Implications for Acid and Metalliferous Drainage Control.

The aim of this study was to determine the combined effect of galvanic interaction and silicate addition on the dissolution of pyrite, the major contributor to acid and metalliferous drainage (AMD). Single (pyrite, sphalerite, and galena)- and bi-sulfide (pyrite-sphalerite and pyrite-galena) batch dissolution experiments were carried out with addition of 0.8 mM dissolved silicate for comparison to previously published data. The pyrite dissolution rate was reduced by 98% upon silicate addition at pH 7.4 with little effect at pH 3.0 and 5.0. The effect of galvanic interaction on reducing pyrite dissolution decreased with increasing pH and was greater in the presence of sphalerite than galena. In contrast, the effect of silicate addition increased with increasing pH and was greater in the presence of galena than sphalerite. The greatest combined effect was at pH 7.4, with <0.1% of pyrite leached in both bi-sulfide systems. Silicate addition also significantly reduced the dissolution of sphalerite or galena (by 10-44%, except at pH 3 for the pyrite-sphalerite system). These results suggest that silicate addition, for reducing both pyrite dissolution and metalliferous drainage, may be applicable at a broad pH in mixed sulfide systems.

Aquatic Phytotoxicity to Lemna minor of Three Commonly Used Drugs of Addiction in Australia.

The manufacturing and consumption of drugs of addiction has increased globally and their widespread occurrence in the environment is an emerging concern. This study evaluated the phytotoxicity of three compounds: methamphetamine, codeine and morphine; commonly reported in Australian urban water, to the aquatic plant Lemna minor under controlled conditions. L. minor was sensitive to lower drug concentrations when administered in multi-compound mixtures (100-500 µg L-1) than when applied individually (range 600-2500 µg L-1), while no adverse effects were observed at environmentally-relevant concentrations (1-5 µg L-1) detected in wastewater effluent. In conclusion, the results show that the concentrations of these compounds discharged into the environment are unlikely to pose adverse phytotoxic effects. These three compounds are known to be the most stable of their group under such conditions indicating that with this respect it is safe to use recycled water for existing regulated reclaimed purposes including agricultural or parklands irrigation or replenishing surface and groundwater. However, more research on the analysis of methamphetamines and opiates in municipal effluents is needed to reassure the likely environmental hazard of these neuroactive drug classes to aquatic organisms. Given the ever-growing production and aquatic disposal of discharge wastewater globally, this study provides timely and valuable insights into the likely drug-related impacts of effluent disposal on aquatic plants in receiving environments.

The Effects of Galvanic Interactions with Pyrite on the Generation of Acid and Metalliferous Drainage.

Although the acid generating properties of pyrite (FeS2) have been studied extensively, the impact of galvanic interaction on pyrite oxidation, and the implications for acid and metalliferous drainage, remain largely unexplored. The relative galvanic effects on pyrite dissolution were found to be consistent with relative sulfide mineral surface area ratios with sphalerite (ZnS) having greater negative impact in batch leach tests (sulfide minerals only, controlled pH) and galena (PbS) having greater negative impact in kinetic leach column tests (KLCs, uncontrolled pH, >85 wt% silicate minerals). In contrast the presence of pyrite resulted consistently in greater increase in galena than sphalerite leaching suggesting that increased anodic leaching is dependent on the difference in anodic and cathodic sulfide mineral rest potentials. Acidity increases occurred after 44, 20, and 12 weeks in the pyrite-galena, pyrite-sphalerite, and the pyrite containing KLCs. Thereafter acid generation rates were similar with the Eh consistently above the rest potential of pyrite (660 mV, SHE). This suggests that treatment of waste rocks or tailings, to establish and maintain low Eh conditions, may help to sustain protective galvanic interactions and that monitoring of Eh of leachates is potentially a useful indicator for predicting changes in acid generation behavior.

Formation of Aluminum Hydroxide-Doped Surface Passivating Layers on Pyrite for Acid Rock Drainage Control.

The aim of this study was to test the performance of a novel method for acid rock drainage (ARD) control through the formation of Al(OH)3-doped passivating surface layers on pyrite. At pH 2.0 and 4.0, there was no obvious inhibition of the pyrite oxidation rate on addition of 20 mg L-1 Al3+ (added as AlCl3·6H2O). In comparison, the pyrite oxidation rate at circumneutral pH (7.4 ± 0.4) decreased with increasing added Al3+ with ≈98% reduction in long-term (282 days) dissolution rates in the presence of 20 mg L-1 Al3+. Al3+ was added to the solution and allowed to equilibrate prior to pyrite addition (2 g L-1). Consequently almost all Al3+ (>99.9%) was initially present as aluminum hydroxide precipitates at pH 7.4. X-ray photoelectron spectroscopy analysis showed a significant concentration of Al3+ (20.3 at. %) on the pyrite surface reacted at pH 7.4 with 20 mg L-1 added Al3+, but no Al3+ on pyrite surfaces reacted at pH 2.0 and 4.0 with added Al3+. Transmission electron microscopy and synchrotron X-ray absorption near edge spectroscopy analyses indicated that compact surface layers containing both goethite and amorphous or nanocrystalline Al(OH)3 formed in the presence of 20 mg L-1 Al3+ at circumneutral pH, in contrast to the porous goethite surface layers formed on pyrite dissolved in the absence of Al3+ under otherwise identical conditions. This work demonstrates the potential for novel Al-based pyrite passivation of relevance to the mining industry where suitable Al-rich waste materials are available for ARD control interventions.

Ecology and performance of aerobic granular sludge treating high-saline municipal wastewater.

The successful development of aerobic granular sludge (AGS) for secondary wastewater treatment has been linked to a dedicated anaerobic feeding phase, which enables key microbes such as poly-phosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms to gain a competitive advantage over floc-forming organisms. The application of AGS to treat high-saline sewage and its subsequent impacts on microbial ecology, however, are less well understood. In this study, the impacts of high-saline sewage on AGS development, performance and ecology were investigated using molecular microbiology methods. Two feeding strategies were compared at pilot scale: a full (100%) anaerobic feed; and a partial (33%) anaerobic feed. The results were compared to a neighbouring full-scale conventional activated sludge (CAS) system (100% aerobic). We observed that AGS developed under decreased anaerobic contact showed a comparable formation, stability and nitrogen removal performance to the 100% anaerobically fed system. Analysis of the microbial ecology showed that the altered anaerobic contact had minimal effect on the abundances of the functional nitrifying and denitrifying bacteria and Archaea; however, there were notable ecological differences when comparing different sized granules. In contrast to previous work, a large enrichment in PAOs in AGS was not observed in high-saline wastewater, which coincided with poor observed phosphate removal performance. Instead, AGS exhibited a substantial enrichment in sulfide-oxidising bacteria, which was complemented by elemental analysis that identified the presence of elemental sulfur precipitation. The potential role for these organisms in AGS treating high-saline wastewater is discussed.

The Formation of Silicate-Stabilized Passivating Layers on Pyrite for Reduced Acid Rock Drainage.

Acid and metalliferous release occurring when sulfide (principally pyrite)-containing rock from mining activities and from natural environments is exposed to the elements is acknowledged as a major environmental problem. Acid rock drainage (ARD) management is both challenging and costly for operating and legacy mine sites. Current technological solutions are expensive and focused on treating ARD on release rather than preventing it at source. We describe here a viable, practical mechanism for reduced ARD through the formation of silicate-stabilized iron oxyhydroxide surface layers. Without silicate, oxidized pyrite particles form an overlayer of crystalline goethite or lepidocrocite with porous structure. With silicate addition, a smooth, continuous, coherent and apparently amorphous iron oxyhydroxide surface layer is observed, with consequent pyrite dissolution rates reduced by more than 90% at neutral pH. Silicate is structurally incorporated within this layer and inhibits the phase transformation from amorphous iron (oxy)hydroxide to goethite, resulting in pyrite surface passivation. This is confirmed by computational simulation, suggesting that silicate-doping of a pseudoamorphous iron oxyhydroxide (ferrihydrite structure) is thermodynamically more stable than the equivalent undoped structure. This mechanism and its controlling factors are described. As a consequence of the greatly reduced acid generation rate, neutralization from on-site available reactive silicate minerals may be used to maintain neutral pH, after initial limestone addition to achieve neutral pH, thus maintaining the integrity of these layers for effective ARD management.

Passivation of pyrite for reduced rates of acid and metalliferous drainage using readily available mineralogic and organic carbon resources: A laboratory mine waste study.

Acid and metalliferous drainage (AMD) is a major environmental issue resulting largely from exposure to weathering of mine wastes containing pyrite (FeS2). At-source strategies to reduce the rate of formation of AMD have potential to be more cost-effective and sustainable than post-generation downstream treatments. The objective of this study was to examine the efficacy of geochemical and microbial treatments for at-source control through pyrite surface passivation. Six kinetic leach columns (KLCs), using a mine waste containing 3.8 wt% pyrite, were subjected to various treatments: 1) untreated, 2) blended calcite, and applications of 3) calcite-saturated water, 4) lime-saturated water followed by calcite-saturated water, 5) biosolids extract water (providing a source of organic carbon to promote microbial growth) and 6) biosolids extract in calcite-saturated water. The untreated KLC leachate pH was on average 5.7 for the first 12 weeks, followed by a gradual decrease to pH 4.5 at week 52. This slow pH decrease is attributed to neutralisation released upon Mg-siderite dissolution. The leachate pH from all treated KLCs was near-neutral at the end of the tests. Pyrite was surface-passivated and leaching supressed by all treatments except for calcite-saturated water. Leaching of Mn and Zn from the untreated waste identified the potential for adverse environmental impact. No evidence was found for surface passivation of Zn- or Mn-containing minerals in the treated KLCs. Blended calcite addition and lime-saturated water followed by calcite-saturated water were most effective at reducing release of Zn and Mn, likely due to precipitation as hydroxides/carbonates.

Inactivation, removal, and regrowth potential of opportunistic pathogens and antimicrobial resistance genes in recycled water systems.

With two thirds of the global population living in areas affected by water scarcity, wastewater reuse is actively being implemented or explored by many nations. There is a need to better understand the efficacy of recycled water treatment plants (RWTPs) for removal of human opportunistic pathogens and antimicrobial resistant microorganisms. Here, we used a suite of probe-based multiplex and SYBR green real-time PCR assays to monitor enteric opportunistic pathogens (EOPs; Acinetobacter baumannii, Arcobacter butzlieri, Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Legionella spp., Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Enteritidis, Streptococcus spp.) and antimicrobial resistance genes (ARGs; qnrS, blaSHV, blaTEM, blaGES, blaKPC, blaIMI, blaSME, blaNDM, blaVIM, blaIMP, blaOXA-48-like, mcr-1 and mcr-3) of key concern from an antimicrobial resistance (AMR), waterborne and foodborne disease perspective. The class 1 integron-integrase gene (intl1) was quantified as a proxy for multi-drug resistance. EOPs, intl1 and ARGs absolute abundance (DNA and RNA) and metabolic activity (RNA) was assessed through three RWTPs with differing treatment trains. Our results indicate that RWTPs produced high quality recycled water for non-potable reuse by removing >95% of EOPs and ARGs, however, subpopulations of EOPs and ARGs survived disinfection and demonstrated potential to become actively growing members of the recycled water and distribution system microbiomes. The persistence of functional intl1 suggests that significant genetic recombination capacity remains in the recycled water, along with the likely presence of multi-drug resistant bacteria. Results provide new insights into the persistence and growth of EOPs, and prevalence and removal of ARGs in recycled water systems. These data will contribute towards the emerging evidence base of AMR risks in recycled water to inform quantitative risk-based policy development regarding water recycling schemes.

The COVID-19 pandemic: Considerations for the waste and wastewater services sector.

This article discusses the potential ramifications of the COVID-19 pandemic on waste and wastewater services, focusing on critical points where alternative operating procedures or additional mitigation measures may be advisable. Key concerns are (i) the long half-life of the virus on materials such as waste containers, bags, and in wastewater, and (ii) possible transmission via contaminated waste surfaces and aerosols from wastewater systems. There are opportunities to further the science of wastewater-based epidemiology by monitoring viral RNA in wastewater to assess disease prevalence and spread in defined populations, which may prove beneficial for informing COVID-19 related public health policy.

Role of microbial diversity for sustainable pyrite oxidation control in acid and metalliferous drainage prevention.

Acid and metalliferous drainage (AMD) remains a challenging issue for the mining sector. AMD management strategies have attempted to shift from treatment of acid leachates post-generation to more sustainable at-source prevention. Here, the efficacy of microbial-geochemical at-source control approach was investigated over a period of 84 weeks. Diverse microbial communities were stimulated using organic carbon amendment in a simulated silicate-containing sulfidic mine waste rock environment. Mineral waste in the unamended leach system generated AMD quickly and throughout the study, with known lithotrophic iron- and sulfur-oxidising microbes dominating column communities. The organic-amended mineral waste column showed suppressed metal dissolution and AMD generation. Molecular DNA-based next generation sequencing confirmed a less diverse lithotrophic community in the acid-producing control, with a more diverse microbial community under organic amendment comprising organotrophic iron/sulfur-reducers, autotrophs, hydrogenotrophs and heterotrophs. Time-series multivariate statistical analyses displayed distinct ecological patterns in microbial diversity between AMD- and non-AMD-environments. Focused ion beam-TEM micrographs and elemental mapping showed that silicate-stabilised passivation layers were successfully established across pyrite surfaces in organic-amended treatments, with these layers absent in unamended controls. Organic amendment and resulting increases in microbial abundance and diversity played an important role in sustaining these passivating layers in the long-term.

The application of life cycle assessment (LCA) to wastewater treatment: A best practice guide and critical review.

Life cycle assessment (LCA) has been widely applied in the wastewater industry, but inconsistencies in assumptions and methods have made it difficult for researchers and practitioners to synthesize results from across studies. This paper presents a critical review of published LCAs related to municipal wastewater management with a focus on developing systematic guidance for researchers and practitioners to conduct LCA studies to inform planning, design, and optimization of wastewater management and infrastructure (wastewater treatment plants, WWTPs; collection and reuse systems; related treatment technologies and policies), and to support the development of new technologies to advance treatment objectives and the sustainability of wastewater management. The paper guides the reader step by step through LCA methodology to make informed decisions on i) the definition of the goal and scope, ii) the selection of the functional unit and system boundaries, iii) the selection of variables to include and their sources to obtain inventories, iv) the selection of impact assessment methods, and v) the selection of an effective approach for data interpretation and communication to decision-makers.

Removal of emerging drugs of addiction by wastewater treatment and water recycling processes and impacts on effluent-associated environmental risk.

Drugs of addiction, have been recognized as potential contaminants of concern to the environment. Effluent wastewater discharge is a major source of contamination to aquatic receiving environments. A year-long monitoring program was undertaken in Australia to characterise the fate of four emerging drugs of addiction: methamphetamine; MDMA; pharmaceutical opioids: codeine and morphine and a metabolite: benzoylecgonine in four wastewater treatment plants operating with different secondary treatment technologies: conventional activated sludge (CAS), membrane bioreactors (MBR), integrated fixed-film AS (IFAS) and sequencing batch reactor (SBR). The effect of subsequent tertiary treatment (coagulation/flocculation) on the removal efficiency was also assessed. Drugs were detected in influent and effluent samples (mean concentration ranged from 43-4777 and 17-1721 ng/L, respectively). Treated effluents had noticeably lower levels compared to raw influents. Removal efficiency of compounds depended on the secondary treatment employed, with IFAS and MBR performing the best with significant removal of compounds (≈90%) followed by CAS (54-96%) and lastly SBR (42-83%). Despite the low levels of drugs measured after the secondary treatment, near complete removal after tertiary treatment (≈99%) was recorded, which demonstrated the effectiveness of using the coagulation/flocculation process as an effective step for enhancing the removal efficiency. The levels of drugs were at a low level in the effluents released into the environment and used for recycling and all posed a low environmental risk in urban water courses based on the risk assessment. The information given here provides new and useful information to the water industry and regulators on the efficiency of drug removal in a range of wastewater treatment configurations.

Occurrence, removal and environmental risk of markers of five drugs of abuse in urban wastewater systems in South Australia.

The occurrence and fate of five drugs of abuse in raw influent and treated effluent wastewater were investigated over a period of 1 year in the Adelaide region of South Australia. Four wastewater treatment plants were chosen for this study and monitored for five drugs which included cocaine in the form of its metabolite benzoylecgonine (BE), methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA) and two opioids (codeine and morphine) during the period April 2016 to February 2017. Alongside concentrations in raw sewage, the levels of drugs in the treated effluent were assessed and removal efficiencies were calculated. Drug concentrations were measured by mixed-mode solid phase extraction and liquid chromatography coupled to a quadrupole mass spectrometer. Drug concentrations detected in the raw wastewater ranged from 7 to 6510 ng/L and < LOD to 4264 ng/L in treated effluent samples. Drug removal rates varied seasonally and spatially. The mass loads of drugs discharged into the environment were in descending order: codeine > methamphetamine > morphine > MDMA > BE. Results showed that all the targeted drugs were on average incompletely removed by wastewater treatment, with removal performance highest for morphine (94%) and lowest for MDMA (58%). A screening-level environmental risk assessment was subsequently performed for the drugs based on effluent wastewater concentrations. Based on calculated risk quotients, overall environmental risk for these compounds appears low, with codeine and methamphetamine likely to pose the greatest potential risk to receiving environments. Given the recognised limitations of current ecotoxicological models and risk assessment methods for these and other pharmaceutical drugs, the potential for environmental impacts associated with the continuous discharge of these compounds in wastewater effluents should not be overlooked.

Comparing the performance of aerobic granular sludge versus conventional activated sludge for microbial log removal and effluent quality: Implications for water reuse.

The application of aerobic granular sludge (AGS) technology has increased in popularity, largely due to the smaller physical footprint, enhanced biological nutrient removal performance and ability to perform with a more stable operation when compared to conventional activated sludge (CAS) systems. To date, the ability of AGS to remove microbial pathogens such as; Escherichia coli, Giardia, and Cryptosporidium has not been reported. This study compared the log10 removal performance of commonly used pathogen surrogates (sulfite-reducing clostridia spores, f-RNA bacteriophage, E. coli and total coliforms) by AGS and CAS during the start-up phase, through to maturation. Results showed that AGS performed as well as CAS for the log10 removal performance of all microbial surrogates, except for spores which were removed more effectively by AGS most likely due to greater adherence of spores to the AGS biomass compared to CAS mixed liquor. Results suggest that AGS is capable of meeting or exceeding CAS-equivalent health-based targets for pathogen removal in the context of water recycling as well as not adversely affecting the secondary effluent water quality (suspended solids, turbidity and particle size) in terms of ultraviolet light transmissivity (254 nm). These findings confirmed for the first time that the adoption of AGS operation would not adversely impact downstream tertiary disinfection processes from altered water quality, nor would it require further pathogen treatment interventions in addition to what is already required for CAS systems.

Dissolved methane in the influent of three Australian wastewater treatment plants fed by gravity sewers.

Methane (CH4) is an important anthropogenic greenhouse gas and a by-product of urban sewage management. In recent years and contrary to international (IPCC) consensus, pressurised (anaerobic) sewers were identified as important CH4 sources, yet relatively little remains known regarding the role of gravity sewers in CH4 production and conveyance. Here we provide the results of a nine month study assessing dissolved CH4 levels in the raw influent of three large Australian wastewater treatment plants (WWTPs) fed by gravity sewers. Similar to recent international research and contrary to IPCC guidance, results show that gravity sewered wastewater contains moderate levels of CH4 (≈1mgL-1). Dissolved CH4 concentration correlated negatively with daily sewage flow rate (i.e. inversely proportional to sewer hydraulic residence time), with daily CH4 mass loads on average some two-fold greater under low flow (dry weather) conditions. Along with sewage hydraulic residence time, sewer sediments are thought to interact with sewage flow rate and are considered to play a key role in gravity sewer CH4 production. A per capita load of 78gCH4person-1y-1 is offered for gravity sewered wastewater entering WWTPs, with a corresponding emission estimate of up to 62gCH4person-1y-1, assuming 80% water-to-air transfer of inflowing CH4 in WWTPs with combined preliminary-primary plus secondary treatment. Results here support the emerging consensus view that hydraulic operation (i.e. gravity versus pressurised, sewage flow rate) is a key factor in determining sewer CH4 production, with gravity sewer segments likely to play a dominant role in total CH4 production potential for large metropolitan sewer networks. Further work is warranted to assess the scale and temporal dynamics of CH4 production in gravity sewers elsewhere, with more work needed to adequately capture and assess the scale of diffuse sewer network CH4 emissions from sprawling urban settlements globally.

Comparison of an anaerobic feed and split anaerobic-aerobic feed on granular sludge development, performance and ecology.

The retrofitting of existing wastewater sequencing batch reactors (SBRs) to select for rapid-settling aerobic granular sludge (AGS) over floc-based conventional activated sludge (CAS), could be a viable option to decrease reactor cycle time and increase hydraulic capacity. Successful CAS-to-AGS conversion has previously been shown to be highly dependent on having a dedicated anaerobic feed, which presents additional engineering challenges when retrofitting SBRs. In this study we compared the performance of a split anaerobic-aerobic (An-Aer) feed with that of a traditional dedicated anaerobic feed regarding AGS formation and stability, nitrogen removal performance and microbial ecology. Using pilot trials, we showed that AGS could be established and maintained when using a split An-Aer feed at low organic loading rates analogous to that of a parallel full-scale conventional SBR. Additionally, we showed that AGS start-up time and nitrogen removal performance were comparable under a split An-Aer feed and dedicated anaerobic feed. Microbial ecology characterisations based on whole-of-community 16S rRNA profiles and targeted analysis of functional genes specific for nitrifying and denitrifying microorganisms, showed that the two different feed strategies had only subtle impacts on both the overall community composition and functional ecology. A much greater divergence in microbial ecology was seen when comparing AGS with CAS. Data presented here will be of value to those planning to retrofit existing CAS-based SBRs to operate with AGS and demonstrates the viability of using a more cost-effective split An-Aer feed configuration over a dedicated anaerobic feed.

Occurrence of illicit drugs in water and wastewater and their removal during wastewater treatment.

This review critically evaluates the types and concentrations of key illicit drugs (cocaine, amphetamines, cannabinoids, opioids and their metabolites) found in wastewater, surface water and drinking water sources worldwide and what is known on the effectiveness of wastewater treatment in removing such compounds. It is also important to amass information on the trends in specific drug use as well as the sources of such compounds that enter the environment and we review current international knowledge on this. There are regional differences in the types and quantities of illicit drug consumption and this is reflected in the quantities detected in water. Generally, the levels of illicit drugs in wastewater effluents are lower than in raw influent, indicating that the majority of compounds can be at least partially removed by conventional treatment processes such as activated sludge or trickling filters. However, the literature also indicates that it is too simplistic to assume non-detection equates to drug removal and/or mitigation of associated risks, as there is evidence that some compounds may avoid detection via inadequate sampling and/or analysis protocols, or through conversion to transformation products. Partitioning of drugs from the water to the solids fraction (sludge/biosolids) may also simply shift the potential risk burden to a different environmental compartment and the review found no information on drug stability and persistence in biosolids. Generally speaking, activated sludge-type processes appear to offer better removal efficacy across a range of substances, but the lack of detail in many studies makes it difficult to comment on the most effective process configurations and operations. There is also a paucity of information on the removal effectiveness of alternative treatment processes. Research is also required on natural removal processes in both water and sediments that may over time facilitate further removal of these compounds in receiving environments.

Towards a comprehensive greenhouse gas emissions inventory for biosolids.

Effective handling and treatment of the solids fraction from advanced wastewater treatment operations carries a substantial burden for water utilities relative to the total economic and environmental impacts from modern day wastewater treatment. While good process-level data for a range of wastewater treatment operations are becoming more readily available, there remains a dearth of high quality operational data for solids line processes in particular. This study seeks to address this data gap by presenting a suite of high quality, process-level life cycle inventory data covering a range of solids line wastewater treatment processes, extending from primary treatment through to biosolids reuse in agriculture. Within the study, the impacts of secondary treatment technology and key parameters such as sludge retention time, activated sludge age and primary-to-waste activated sludge ratio (PS:WAS) on the life cycle inventory data of solids processing trains for five model wastewater treatment plant configurations are presented. BioWin(®) models are calibrated with real operational plant data and estimated electricity consumption values were reconciled against overall plant energy consumption. The concept of "representative crop" is also introduced in order to reduce the uncertainty associated with nitrous oxide emissions and soil carbon sequestration offsets under biosolids land application scenarios. Results indicate that both the treatment plant biogas electricity offset and the soil carbon sequestration offset from land-applied biosolids, represent the main greenhouse gas mitigation opportunities. In contrast, fertiliser offsets are of relatively minor importance in terms of the overall life cycle emissions impacts. Results also show that fugitive methane emissions at the plant, as well as nitrous oxide emissions both at the plant and following agricultural application of biosolids, are significant contributors to the overall greenhouse gas balance and combined are higher than emissions associated with transportation. Sensitivity analyses for key parameters including digester PS:WAS and sludge retention time, and assumed biosolids nitrogen content and agricultural availability also provide additional robustness and comprehensiveness to our inventory data and will facilitate more customised user analyses.

Understanding the impacts of allocation approaches during process-based life cycle assessment of water treatment chemicals.

Chemicals are an important component of advanced water treatment operations not only in terms of economics but also from an environmental standpoint. Tools such as life cycle assessment (LCA) are useful for estimating the environmental impacts of water treatment operations. At the same time, LCA analysts must manage several fundamental and as yet unresolved methodological challenges, one of which is the question of how best to "allocate" environmental burdens in multifunctional processes. Using water treatment chemicals as a case study example, this article aims to quantify the variability in greenhouse gas emissions estimates stemming from methodological choices made in respect of allocation during LCA. The chemicals investigated and reported here are those most important to coagulation and disinfection processes, and the outcomes are illustrated on the basis of treating 1000 ML of noncoagulated and nondisinfected water. Recent process and economic data for the production of these chemicals is used and methodological alternatives for solving the multifunctionality problem, including system expansion and mass, exergy, and economic allocation, are applied to data from chlor-alkali plants. In addition, Monte Carlo simulation is included to provide a comprehensive picture of the robustness of economic allocation results to changes in the market price of these industrial commodities. For disinfection, results demonstrate that chlorine gas has a lower global warming potential (GWP) than sodium hypochlorite regardless of the technique used to solve allocation issues. For coagulation, when mass or economic allocation is used to solve the multifunctionality problem in the chlor-alkali facility, ferric chloride was found to have a higher GWP than aluminum sulfate and a slightly lower burden where system expansion or exergy allocation are applied instead. Monte Carlo results demonstrate that when economic allocation is used, GWP results were relatively robust and resilient to the changes in commodity prices encountered during the study period, with standard deviations less than 6% for all chlor-alkali-produced chemicals reported here. Overall outcomes from the study demonstrate the potential variability in LCA results according to the allocation approach taken and emphasize the need for a consensus approach to water sector LCAs.

Municipal gravity sewers: an unrecognised source of nitrous oxide.

Nitrous oxide (N2O) is a primary ozone-depleting substance and powerful greenhouse gas. N2O emissions from secondary-level wastewater treatment processes are relatively well understood as a result of intensive international research effort in recent times, yet little information exists to date on the role of sewers in wastewater management chain N2O dynamics. Here we provide the first detailed assessment of N2O levels in the untreated influent (i.e. sewer network effluent) of three large Australian metropolitan wastewater treatment plants. Contrary to current international (IPCC) guidance, results show gravity sewers to be a likely source of N2O. Results from the monitoring program revealed hydraulic flow rate as a strong driver for N2O generation in gravity sewers, with microbial processes (nitrification and possibly denitrification) implicated as the main processes responsible for its production. Results were also used to develop a presumptive emission factor for N2O in the context of municipal gravity sewers. Considering the discrepancy with current IPCC Guidelines, further work is warranted to assess the scale and dynamics of N2O production in sewers elsewhere.