Goen Ho

Biofilters used for the conversion of odorous hydrogen sulphide to odourless sulphate in wastewater treatment plants are known to generate large volumes of unusable weakly sulphuric acidic leachate. This paper presents a novel biofilter that produces small-volume and high-concentration sulphuric acid (H2SO4) as a useful product. The concentrated H2SO4 was produced by washing down the up-flow biofilter with an optimum amount of nutrient solution at pre-determined intervals which created a moisture and pH gradient within the biofilter resulting in an environment at the top favourable for the bacterial conversion of H2S, while concentrated sulphuric acid was accumulated at the base. A lab-scale biofilter based on this concept achieved 95 % H2S removal efficiency with a maximum H2S elimination capacity of 16.3 g/m3/h. Only small volumes (1 mL/L reactor/day) of concentrated sulphuric acid (>5.5 M) was produced after 150 days of continuous operation. A pilot-scale trial at a local WWTP not only achieved similar result to that of the lab-scale trial, but the concentrated sulphuric acid also stripped co-contaminant NH3 from the incoming air resulting in a simultaneous removal of H2S and NH3 with ammonium sulphate as a product in the leachate that can be harvested for further use.

A desktop study examined water meter readings of secondary schools in the Perth metropolitan area of Western Australia. From this, a suitable metric for measuring water use in secondary schools was determined. Water use quartiles on a per person basis were also calculated based on 70 secondary schools and benchmarks were established. In addition, a water audit of 9 high water using secondary schools (>20,000 kL/a) was performed to identify key areas where water is used and where water savings can be made. Total water use of these schools decreased by 13% in the 12 months following the completion of the water audits. Having determined water use averages, benchmarks and key areas for water savings, the education industry can make informed decisions about their water use and how to increase efficiency at the schools.

The essential connection between energy and water, also defined as the energy-water nexus, has been recognized by scientists and policy makers worldwide. Integrated solutions and policies that consider both energy and water aspects into future planning have been developing at a fast pace. In this paper, we review the state of the art of the energy-water nexus, with particular focus on the integration between renewable energy and desalination technologies. We also model the integration of reverse osmosis (RO) desalination and solar photovoltaics in an edge-of-grid coastal town in Western Australia. The current literature agrees on the sustainable use of renewable energy sources to improve the water-energy nexus in the context of water desalination. Although the integration of solar and wind energy with desalination technologies is a mature and well-proven solution at both small and large scales, the intermittency and fluctuating nature of wind and solar power still constitute the main technical challenge that has limited the diffusion of renewable energy powered desalination on a large scale. Several successful applications of renewable energy powered desalination in remote, off the grid, locations have tackled the issue of power intermittency by the use of batteries and diesel generators. Such systems often couple reverse osmosis desalination with solar photovoltaic energy. Large desalination plants have been successfully connected to wind farms and grid electricity to secure uninterrupted plant operations, thus meeting water targets in large-scale systems. Our review identifies a knowledge gap in the integration of decentralized energy systems, e.g. rooftop solar photovoltaic, with small scale RO desalination. Such configuration would benefit those regional towns that have historically suffered from weak and unreliable connections to the electricity grid, thus helping them secure both their energy and water requirements. The modelling exercise on a renewable energy powered RO plant in an edge-of-grid town in Western Australia has identified an operating strategy that maximizes the renewable energy fraction and secures the annual supply of water. The system involves operating the RO unit for six months of the year at a daily variable load and integrating solar energy with grid electricity. Careful evaluation of the RO performance under such operating conditions is necessary to ensure a safe and reliable water treatment process. A niche in the literature of the energy-water nexus has been identified in the integration of rooftop solar photovoltaic, grid electricity and desalination technologies applied in a regional context. A future study will consider the rollout of rooftop solar photovoltaic installations across the whole town, thus enabling the active engagement of the community by integrating the households’ energy demand response patterns to the operations of both rooftop photovoltaics and the desalination unit.

Solid waste management in Pacific Island countries was reviewed. Shortcomings were identified to be due to the underlying public health paradigm that was a legacy of colonial governments and the legislation, regulation, institution and practices that were based on it. The environmental protection paradigm introduced later through the initiative of the Pacific regional cooperation has added has added a desirable dimension, but lack of capacity building has resulted in landfilling continuing as the primary means of disposal. Field survey was conducted in Honiara to survey waste managers and stakeholders and to determine household waste and city market waste generation, and pathways of waste electric and electronic equipment and aluminium cans. These suggest that a pragmatic system paradigm could assist with governments and households to better manage wastes.

Fouling caused by extracellular polymeric substances (EPS), the products secreted by bacteria, has been regarded as one of significant contributors to deteriorating membrane separation performances. Most current laboratory studies on membrane fouling use selected model foulants, such as alginate, which may not typically represent bacteria-produced EPS. This study aimed to compare the fouling caused by naturally occurring EPS and commercial polysaccharides in forward osmosis (FO) separation, thus possibly suggesting the ideal polysaccharide model in the research of membrane fouling. Three types of commercial polysaccharides, namely alginate, xanthan and pullulan, as well as two types of EPS (EPS-RSW and EPS-FSW) extracted from the bacteria in raw seawater and filtered seawater (RSW 14 and FSW 6) were selected herein. Our results showed that the commercial polysaccharides and the naturally occurring EPS behaved differently in the FO fouling tests, which could be largely attributed to the difference in their solution viscosities. Both of the solutions consisting of EPS exhibited lower viscosities and led to higher permeate fluxes, in comparison to those of the solutions with the commercial alginate and xanthan polysaccharides. The use of pullulan caused the most similar flux change in FO separation to that by utilizing the EPS; thereby we suggest that pullulan be the preferred model polysaccharide to represent EPS in FO fouling research.

Recent research into conversion of organic wastes at Murdoch University is reviewed to highlight interlinkages, insights gained and potential future research. Central to the research underpinning the success of the one vessel sequential aerobic (to bring temperature to thermopilic)-anaerobic (to extract methane)-aerobic (to produce compost) thermophilic process is utilising the concept of electron transfer, which links aerobic and anaerobic phases through electrons as a common currency. This concept is consistent with our ability to produce electricity from the process liquor using a microbial fuel cell. Management of the liquor has been found to be critical as it is a carrier of micro-organisms that perform all the biological processes in the reactor and assist with start up. Start up has also been facilitated by the presence of grass clippings in MSW. Linkages to nitrogen removal, unusual properties of liquor, grass clippings and possible pre-treatment of cellulose wastes using fungus are highlighted.

This study investigates odour removal of pilot-scale biofilters treating volatile organic compounds (VOCs) produced during composting of organic fraction of municipal solid wastes (OFMSW). Four biofilters, containing non-biodegradable zeolite, biodegradable coir fibre, and the mixture of both materials, with and without inoculum, were set up onsite to treat the exhaust gases from a local composting facility. Odour-removal efficiencies of the biofilters were monitored by sensory concentration measurement using olfactometry and analytical measurement using gas chromatography-mass spectrometry (GC-MS) on three occasions, at start-up, 3 months and 9 months of operation. At feeding rate of 1 L/L/min and feed concentration of 9,000-10,000 OU, odour removal efficiencies of the biofilters were over 90% right from start up through to 9-month period of monitoring. Inoculation of biofilter was found to be beneficial but not essential. Based on detailed analysis of odour compounds using GC-MS, zeolite biofilter was effective in adsorbing polar compounds (such as alcohol and volatile acids) while coir biofilter was found to be particularly effective in capturing non-polar VOCs, such as monoterpenes (the main component in the feed stream). The combination of coir and zeolite complemented one another providing very effective removal of both polar and non-polar volatile compounds.

Biofouling is the single most important issue in reverse osmosis sea water desalination worldwide (Ridgway et al., 1999) and may account for up to 50% of energy use. Which species are responsible and their origin is unclear. With the advent of next generation sequencing, species diversity and transience can be examined at orders of magnitude greater detail than was previously possible. We found many similarities in bacterial families across source water, prefiltration units and membranes in this study and in the few other studies available, despite disparate locations and seasons. Key groups included members of the Bacteroidetes (e. Flavobacteriaceae), Planctomycetes, Alphaproteobacteria (eg. Rhodobacteraceae, Sphingomonadales), Betaproteobacteria (eg. Burkholderia) and Gammaproteobacteria (eg. Oceanospirillales, Xanthomonadaceae). Despite similarities in families, the predominant fouling species on reverse osmosis (RO) membranes appear to differ between studies. This seems likely to reflect a common origin (seawater) but subsequent adaptation or selective pressures in different niches, particularly on RO membranes under high pressure and salt concentration. We can now select environmental isolates from our culture collection representing key bacterial groups responsible for biofouling in seawater systems. This will enable more accurate evaluation of the effectiveness of anti-fouling strategies.

The design and development of a novel biofilter is described in this paper. Moisture control is a key aspect of the design. Moisture from the gas stream leaving the biofilter is condensed and returned to the top of biofilter as reflux of pure water. The refluxed water maintains a moist environment for the bacteria throughout the total biofilter column. It also washes down microbial product/s (nitrite and nitrate in the case of ammonia oxidation) that may be toxic to microorganism at a high concentration. This allows microbial activity to be maintained at its most favorable level in the top section of the biofilter. Optimization of moisture balance between evaporation and condensation can result in a system whereby water level on the media surface is sufficient for microbes to thrive while no leachate is produced. In a proof-of-concept study, a laboratory-scale computer controlled biofilter system employing the reflux process was operated to remove ammonia from an air stream (2.05 μmol /L= 50 ppmv) at a volume load of 1 L/L/min. Inoculated zeolite (clinoptilolite) was used as filter media. Depth profile analysis of the filter bed showed the development of a steep gradient of ammonia, nitrite and nitrate from the top layer to the bottom layer of filter media in the biofilter. Aside from the well-known ammonium adsorption on zeolite, consistent microbial nitrification continued to take place. Nitrite and nitrate level at the bottom of the biofilter continued to increase over 180 day period of experiment. As a result, ammonia removal efficiency remained close to 100% in the leachate-free biofilter.

Top-down sanitation programs that promote a specific sanitation technology based on the presumptions of 'outside experts' have been criticised for endorsing unsustainable, expensive and inappropriate technologies. In response to these failings, a new era of demand-led sanitation programs (including community-led total sanitation and sanitation marketing) encourage greater participation of users to create appropriate sanitation technologies. This paper examines the use of participatory design sessions with local builders and householders in three rural districts in Malawi. The paper provides an account of the participatory design methodology and critically reflects on the processes and challenges in relation to power, creativity and ownership. The designs created during the sessions are presented with recommendations for further testing and structural refinement.