• Energy Research

Energy use in households, including private transport, accounts for about 30% of primary energy use in industrialised countries. Therefore, households are important key drivers of energy use and related greenhouse gas emissions. In order to understand energy use related to water in households a detailed mathematical flow analysis of materials, energy, CO 2 emissions and costs (MMFA) for household water use was set up and tested for a specific family household in Brisbane, Australia. The simulation results for the current state of this household were well within 20% of the monitored data. After calibration, a detailed scenario investigation determined the impact of (i) potential and (ii) realistic reduction values for all relevant (a) behavioural and (b) technical parameters, including a shift from gas to a solar hot-water system. The reduction potentials for water use, greenhouse gas emissions, water-related energy consumption, water costs and water-related energy costs were 4-77%, 14-85%, 15-93%, 1-31% and 13-90% respectively. The study showed that for this household, technical improvements alone, without changing to a solar hot-water system, result in less than a 15% change in terms of energy and greenhouse gas emissions. In contrast, combined behavioural and technical changes have a much higher reduction potential.

This paper explores the range of potential energy use impacts of shower water demand management in a case study of five highly characterised households in Melbourne (Australia), and assesses the difference in energy and cost responses for four different hot water system types. Results show that a shift to four minute showers (from current durations of between six and ten minutes) would lead to a reduction of between 0.1 and 3.8 kWh p(-1) d(-1) in the households studied, comprising between 9% and 64% of baseline hot water system energy use. Contrasted with an average energy use for water service provision in Melbourne of 0.3 kWh p(-1) d(-1), such household reductions demonstrate significant potential for urban water cycle energy management. Combined water and energy (natural gas) cost savings in response to the four-minute shower scenario were $37 to $500 hh(-1) y(-1) in the households studied. Energy cost savings would be more significant for households with electric storage hot water systems than those with gas systems, at $39 to $900 hh(-1) y(-1), due to higher variable tariffs for electricity than natural gas in Victoria ($0.2678 kWh(-1) vs $0.0625 kWh(-1)). Households with electric storage hot water systems may therefore have greater financial incentive to participate in water-related energy demand management (assuming similar tariff structures). (c) 2017 Elsevier Ltd. All rights reserved.

The aim of this work was to demonstrate at pilot scale a high level of energy recovery from sewage utilising a primary Anaerobic Migrating Bed Reactor (AMBR) operating at ambient temperature to convert COD to methane. The focus is the reduction in non-renewable CO(2) emissions resulting from reduced energy requirements for sewage treatment. A pilot AMBR was operated on screened sewage over the period June 2003 to September 2004. The study was divided into two experimental phases. In Phase 1 the process operated at a feed rate of 10 L/h (HRT 50 h), SRT 63 days, average temperature 28 degrees C and mixing time fraction 0.05. In Phase 2 the operating parameters were 20 L/h, 26 days, 16 degrees C and 0.025. Methane production was 66% of total sewage COD in Phase 1 and 23% in Phase 2. Gas mixing of the reactor provided micro-aeration which suppressed sulphide production. Intermittent gas mixing at a useful power input of 6 W/m(3) provided satisfactory process performance in both phases. Energy consumption for mixing was about 1.5% of the energy conversion to methane in both operating phases. Comparative analysis with previously published data confirmed that methane supersaturation resulted in significant losses of methane in the effluent of anaerobic treatment systems. No cases have been reported where methane was considered to be supersaturated in the effluent. We have shown that methane supersaturation is likely to be significant and that methane losses in the effluent are likely to have been greater than previously predicted. Dissolved methane concentrations were measured at up to 2.2 times the saturation concentration relative to the mixing gas composition. However, this study has also demonstrated that despite methane supersaturation occurring, micro-aeration can result in significantly lower losses of methane in the effluent (<11% in this study), and has demonstrated that anaerobic sewage treatment can genuinely provide energy recovery. The goal of demonstrating a high level of energy recovery in an ambient anaerobic bioreactor was achieved. An AMBR operating at ambient temperature can achieve up to 70% conversion of sewage COD to methane, depending on SRT and temperature.

To date, key water–energy connections have not been systematically quantified. Nor has their potential for contributing to greenhouse gas mitigation been evaluated. Lack of knowledge of these links, particularly within cities, is viewed as a major limitation to energy-sensitive urban water management and integrated urban design. This paper fills part of this void. The key contribution is a new conceptual model coupled with a systematic review of the connections of influence. Drawing on Australian and international data, the results provide a structured estimate of water-related energy use and associated emissions in a hypothetical city of 1,000,000 people. This demonstrates that water-related energy use accounts for 13% of total electricity and 18% of the natural gas used by the population in the average case. This represents 9% of the total primary energy demand within Australia or 8% of total national territorial greenhouse gas emissions. Residential, industrial and commercial water-related energy use constitutes 86% of water-related greenhouse gas emissions. We conclude that urban water is a significant and overlooked lever that could significantly influence urban energy consumption.

The methane yield from the digestion of algae is typically much lower than the theoretical methane yield, and lower than yields reported for other organic substrates. This study presents a novel free nitrous acid (FNA) pre-treatment technique to improve methane production from algal biomass. The methane production yield through anaerobic digestion was found to be dramatically enhanced by FNA pre-treatment (2.31 mg HNO2–N L−1), with a 51% increase in the methane yield (from 161 to 250 L CH4 per kg VS added). A two substrate model was used to describe the apparent presence of rapid and slowly degradable material. Model-based analysis revealed that with FNA pre-treatment (2.31 mg HNO2–N L−1), the availability of both rapid and slowly biodegradable substrates were increased. Higher levels of nitrite (159 and 1006 mg N L−1) had an inhibitory/toxic effect. For this reason, coupled with the fact that denitrification of nitrite consumes organic substrate, it is concluded that pre-treatment liquor should be removed before digestion.

Abstract Indoor air pollution, caused by solid cooking fuels, is the fourth largest global contributor to premature death, equivalent to unsanitary water, and greater than malaria. Therefore, the Indian government currently subsidises replacement of these fuels with cleaner burning Liquefied Petroleum Gas (LPG), but an import dependency makes this program vulnerable to oil price shocks and supply disruption. The blending of LPG with dimethyl ether (DME), produced from domestically available feedstocks, may be one means of reducing this vulnerability. In the context of pursuing a low carbon future, this study investigates the use of CO2 released during ethanol production, combined with hydrogen gained by water electrolysis from renewable electricity, for this purpose. More than 85% of India's ethanol is produced in five states, four of which are richly endowed with a renewable electricity generation potential. The estimated cost of DME produced in this manner is significantly above a historically high LPG price but may become viable in the EIA's “high oil price” scenario if future (US DOE) electrolysis performance targets are achieved, and at electricity costs below $45 per MWh.

Abstract Residential resource use efficiency and management is a subject of interest to a number of fields spanning the physical and social sciences. Energy use for residential water heating in Australia is some five to eleven times more than the energy required to deliver urban water services. However, little is known about which activities within households contribute most significantly to water-related energy use (WRE). This work quantifies WRE use in individual households, and identifies household characteristics which contribute significantly to variation. Empirical data were collected through in-home audits, interviews and high-resolution end-use water flow meters for five households in Melbourne, and two in Brisbane, Australia. This was used to characterise 139 parameters describing household occupancy characteristics, behaviours, technologies, and structural and environmental aspects of influence. Mathematical material flow analysis (MMFA) modelling was conducted for individual water and energy use subsystems within each household. WRE use ranged from 7 to 21 kWh hh −1 d −1 (13–24% of total household energy use in Melbourne and 76–79% in Brisbane). Detailed end use analysis of the five Melbourne households showed that shower use (11–61% WRE), hot water system efficiency losses (8–31% WRE) and clothes washer usage (4–17% WRE) contributed most to differences in WRE between households. Findings highlighted shower use as a consistent influence on WRE across households, and suggest further investigation of shower programs as a potentially effective demand management measure for both water and energy in households. The work highlights the importance of consistent messaging for both water and energy efficiency, and suggests that a focus on both human and technical characteristics of households is needed for effective management of combined water and energy use.

Abstract An important energy poverty reduction initiative in India is aimed at replacing the use of solid cooking fuels with cleaner burning Liquefied Petroleum Gas (LPG). Projections suggest however that India will become increasingly dependent on LPG imports, the cost of which is strongly linked to the prevailing oil price and associated volatility. Dimethyl ether (DME) is a synthetic fuel which may be manufactured from domestically available carbonaceous feedstocks, and is compatible with blending with LPG. Very large quantities of Municipal Solid Waste (MSW) are generated in India's metropolitan cities, 90% of which is disposed of onto unsanitary landfills, creating major environmental and health concerns. This article investigates the techno-economic merits of reducing these impacts by using a portion of the MSW generated in Kolkata (in the form of a Refuse Derived Fuel (RDF)) to produce DME. Results suggest that the production of DME from a 50:50 blend of locally available coal and RDF (comprising 10% of the MSW placed at Kolkata's main landfill) will enable the supply of a clean cooking fuel to approximately 15% of Kolkata's population, and become cost competitive with imported LPG at an Indian basket oil price of $130 per barrel. Results also suggest that, at this blend ratio, the fossil fuel derived greenhouse gas emissions at the DME production plant will be more than offset by landfill methane emissions avoided using the RDF.

Ammonia-oxidising bacteria (AOB) are a major contributor to nitrous oxide (N(2)O) emissions during nitrogen transformation. N(2)O production was observed under both anoxic and aerobic conditions in a lab-scale partial nitritation system operated as a sequencing batch reactor (SBR). The system achieved 55 ± 5% conversion of the 1g NH(4)(+)-N/L contained in a synthetic anaerobic digester liquor to nitrite. The N(2)O emission factor was 1.0 ± 0.1% of the ammonium converted. pH was shown to have a major impact on the N(2)O production rate of the AOB enriched culture. In the investigated pH range of 6.0-8.5, the specific N(2)O production was the lowest between pH 6.0 and 7.0 at a rate of 0.15 ± 0.01 mg N(2)O-N/h/g VSS, but increased with pH to a maximum of 0.53 ± 0.04 mg N(2)O-N/h/g VSS at pH 8.0. The same trend was also observed for the specific ammonium oxidation rate (AOR) with the maximum AOR reached at pH 8.0. A linear relationship between the N(2)O production rate and AOR was observed suggesting that increased ammonium oxidation activity may have promoted N(2)O production. The N(2)O production rate was constant across free ammonia (FA) and free nitrous acid (FNA) concentrations of 5-78 mg NH(3)-N/L and 0.15-4.6 mg HNO(2)-N/L, respectively, indicating that the observed pH effect was not due to changes in FA or FNA concentrations.