G. Ho

The role of indigenous microorganisms in suppression of Salmonella regrowth in composted biosolids.

Composting is commonly used as an effective means of stabilizing wastewater biosolids and reducing pathogens to very low concentrations. However, it has been shown that under certain conditions Salmonella can regrow in previously composted biosolids. Growth of seeded Salmonella typhimurium in composted biosolids ranging from two weeks to two years maturity was monitored. Results from sterile and non-sterile composted biosolids were compared. Seeded S. typhimurium colonized rapidly in sterilized biosolids reaching a maximum population density of more than 10(8) g(-1). Growth of seeded S. typhimurium was suppressed in non-sterilized compost with a maximum population density of less than 10(3) g(-1). There was a significant decline in the growth rate of seeded Salmonella in sterilized compost when the compost was stored, suggesting that bio-available nutrients declined with storage. However, in non-sterilized compost this was not the case. This suggests that the indigenous microflora play a significant role in suppression of Salmonella regrowth in composted biosolids. There was a strong negative correlation (-0.85) between the Salmonella inactivation rate and the maturity of compost in non-sterilized compost. The Salmonella inactivation rate was seven times higher in biosolids composting for two weeks as compared to compost stored for two years. This suggests that the antagonistic effect of indigenous microorganisms towards Salmonella declined with compost storage. It was concluded that all composted biosolids had a Salmonella regrowth potential. However, the indigenous microflora significantly reduced this regrowth potential. Long-term storage of compost is not recommended as this may increase the pathogen regrowth potential.

Effects of gypsum and sewage sludge amendment on physical properties of fine bauxite refining residue

The poor soil structure and low hydraulic conductivity of fine bauxite refining residue (red mud) from alumina production are the major factors hindering its revegetation. Red mud, disposed of by the dry stacking-method, was amended with gypsum (38.5 and 77 t/ha) and sewage sludge (38.5, 77, and 144 t/ha) to evaluate their effects on soil physical properties in a field experiment. Sewage sludge amendment significantly reduced soil bulk density (25%) and particle density (9%), and increased the total porosity of red mud (8%). Both sewage sludge and gypsum contributed to the increases in hydraulic conductivity of red mud (from 1.3 to 24 x 10-5 m/s) after one growing season. Plant cover percentage and dry weight yield of Agropyron elongatum increased with an increase in gypsum and sewage sludge amendment. Plant growth did not significantly affect soil physical properties, but the enhanced growth was due to improved soil structure and hydraulic conductivity. An application of 77 t/ha gypsum and 144 t/ha sewage sludge exerted the maximum effect on soil physical properties of red mud and should ensure the initial establishment of plants.

Ethanol from lignocellulose using crude unprocessed cellulase from solid-state fermentation.

It was desired to study a simplified method of cellulase production using solid-state fermentation for its potential to be used on-site as part of a cellulose to ethanol conversion process, in lieu of expensive and energy intensive commercial enzyme preparations. Crude unprocessed cellulase extracts were produced by solid-state fermentation of Trichoderma reesei on ground wheat straw. While cellulase yields were not high they were sufficient to produce ethanol from wheat straw in simultaneous saccharification and fermentation with Saccharomyces cerevisiae. As little as an additional 5% of the material converted to ethanol may be employed for cellulase production suggesting an inordinate quantity of additional substrate would not be required. These findings suggest a simplified crude cellulase process at the site of ethanol production using a common lignocellulosic substrate may be employed in lieu of commercial enzyme preparations.

Novel methanogenic rotatable bioelectrochemical system operated with polarity inversion

A novel membraneless bioelectrochemical system termed rotatable bioelectrochemical contactor (RBEC) was fabricated and evaluated for its ability to recover useful energy (here methane) from a low organic strength wastewater. We studied the operational characteristics of the RBEC by operating it as a three-electrode electrolysis cell. A stack of conductive disks (each subdivided into two half disks), similar to rotating biological contactors, were rotated with one-half disk immersed in the wastewater and the other into the gas headspace. By carrying out regular half rotations (180° rotation) the anode became the cathode and vice versa. This operation resulted in the build-up of a biofilm that could catalyze both an anodic acetate oxidation and a cathode-driven methanogenesis. Methane production rate was directly proportional to the applied electrical energy. Increase in current density (from 0.16 to 4.1 A m(-2)) resulted in a faster COD removal (from 0.2 to 1.38 kg COD m(-3) day(-1)) and methane production (from 0.04 to 0.53 L L(-1) day(-1)). Of the electrons flowing across the circuit, over 80% were recovered as methane. Such methane production was electrochemically driven by the headspace-exposed cathodic half disks, which released the methane directly to the gas-phase. Energy analysis shows that the new design requires less energy for COD removal than what is typically required for oxygen supply in activated sludge processes. Because the system could operate without wastewater recirculation against gravity; additional pH buffer chemicals; ion-exchange membranes or electrochemical catalysts, it has desirable characteristics for process up-scale. Further, the current report shows the first example of a BES with identical biofilm (due to intermittent polarity inversion) on both electrodes.

The effects of clay amendment and composting on metal speciation in digested sludge

Sewage sludge usually contains significant heavy metals that may limit its land application. Heavy metals in municipal solid waste have been shown to be less mobile by amendment with bauxite refining residue (red mud) prior to the composting process. In the present research a sequential step extraction was employed to investigate metal speciation (into exchangeable, bound to carbonate, to Mn and Fe oxides, to organic matter and in residue phase) and the effect of red mud on metal speciation in compost of sewage sludge for Cr, Cu, Ni, Pb and Zn. The effect of red mud addition and composting process on metal distribution in sewage sludge compost is significant. Red mud addition generally reduces metal leachability and therefore the potential hazard of releasing metals from sludge compost through adsorption and complexation of the metals on to inorganic components to different extents for the different metals. Red mud cannot desorb, however, metals bound to organic matter in the sludge. The composting process breaks down organic matter in the sludge and may release the heavy metals. The addition of red mud prior to the sludge composting binds the released metals on to the red mud for those not strongly readsorbed by the remaining organics (Cu, Ni and Zn).

Selection of Salmonella typhimurium as an indicator for pathogen regrowth potential in composted biosolids.

In order to select a suitable indicator for monitoring the pathogen regrowth potential of composted biosolids, the growth kinetics of selected bacteria were investigated. Growth parameters of six serovars of Salmonella and three strains of Escherichia coli in sterilized compost were compared. Seeded Salmonella and E. coli grew rapidly, reaching population densities of more than 108 g−1 after 30 h of incubation. The specific growth rates of Salmonella serovars and E. coli strains were similar and varied from 0·49 to 0·55 h−1. The specific growth rate of the Salm. Typhimurium isolates was significantly higher than the other bacterial strains. It was concluded that an antibiotic‐resistant strain of Salm. Typhimurium can be used as an indicator for a pathogen regrowth potential test.

Sewage sludge as organic ameliorant for revegetation of fine bauxite refining residue

The rise in aluminium demand in the world has significantly increased the generation of bauxite residue which occupies huge areas of land worldwide. Direct revegetation of residue storage areas has been unsuccessful because of the high alkalinity and salinity, and poor nutrient contents of the fine residue (red mud). This paper describes glasshouse and field experiments evaluating the potential use of sewage sludge as an organic ameliorant for gypsum amended red mud. The growth of Agropyron elongatum in red mud receiving gypsum (0 and 38.5 t ha-1) and sewage sludge (0, 38.5 and 77 t ha-1) amendment was assessed in a glasshouse study. Leachate and soil analyses revealed that gypsum was effective in reducing the pH, EC and ESP of red mud, while sewage sludge gave additional reductions in EC, Na and ESP. No evidence of any significant increases in heavy metal contents were observed in the leachates following sewage sludge amendment. However, soil Al contents were more available in red mud receiving only sewage sludge treatment. Sewage sludge amendment significantly increased dry weight yield and provided sufficient nutrients for plant growth except K which was marginal. No heavy metal accumulation was observed in Agropyron. Following that, a field experiment was performed having red mud amended with sewage sludge (38.5, 77 and 154 t ha-1) and gypsum (38.5 and 77 t ha-1) to evaluate their effects on soil physical properties of red mud. Sewage sludge significantly reduced soil bulk density (25%) and particle density (9%) and increased the total porosity of red mud (8%). Hydraulic conductivity also increased from 1.5 to 23 x 10-5 m s-1. Plant cover percentage and dry weight yield of Agropyron increased with an increase in gypsum and sewage sludge amendment. The results confirm that sewage sludge is effective in improving both soil structure and nutrient status of gypsum amended red mud. The use of sewage sludge for red mud revegetation provides not just an option for sludge disposal, but also a cost effective revegetation strategy for bauxite refining industry.

Development of a reliable low-cost reverse osmosis desalination unit for remote communities

Research was carried out for two years to investigate the potential of using renewable energy pumped reverse osmosis (RO) for ground water desalination in remote Aboriginal communities of Australia. This has resulted in the development of a prototype pilot scale, low-pressure, wind-powered RO system. This paper presents the prototype design, construction and field testing to determine the quantity and quality of desalinated water produced and the reliability of the prototype operating under field conditions. Conclusions are drawn as to the operating requirements for use with typical Western Australian ground waters and in the Aboriginal community setting.

Integrated waste management

The concept of integrated waste management (IWM) has been developed to provide a means towards sustainability. Population growth coupled with increasing consumption have increased the amount of waste generated across the world while also facilitating the use of IWM to divert waste from landfill toward more long-term sustainable options such as reuse and recycling programmes — programmes that also maintain the longevity of a products life and reduce pressure on natural resources (Figure 26.1) (Ami et al., 2002). The other major factor influencing the formation of IWM strategies is social pressure Huang et al., 2001), Social pressure has been found to cause authorities to implement IWM strategies even where landfill space is available Barth. 2000) and has originated with increased education levels among consumers about current unsustainable and sustainable waste practices (Clarke et al., l99; Huang et al., 2001). The success of IWM strategies is largely attributed to the degree of social acceptance, such that the landfill problem associated with high population density areas has been found to stem from a low social acceptance of reuse and recycling programmes, rather than their absence (Ami et al.. 2002; Bradshaw and Ozores-Hampton, 2002: Mohee, 2002: Poon et al., 2001). An assessment of the social acceptance of IWM strategies is now a precursor for most new programmes and the technologies chosen for 1W M may he dependent on social factors (Kwawe, 2002).

The role of the submergent macrophyte Triglochin huegelii in domestic greywater treatment

Conventional reedbed systems, which are used in wastewater treatment, are little more than monocultures of Phragmites, Baumea, Water Hyacinth (Eichhornia crassipes), Typha or Schoenoplectus. Pond systems, employing a wider range of species, are a means to recycle more nutrients, improve treatment potential and mirror natural ecosystems in ways to sustain the ecosystem. Species of Triglochin, commonly known as water ribbons throughout coastal Australia, are fast-growing submergent macrophytes which seem to be adapted to high nutrient concentrations. In Western Australia, Triglochin huegelii is mainly a submergent plant but its leaves tend to float on the surface in shallow waterways and it has been found seasonally in some ephemeral swamps and lakes. As water receedes, the leaves become emergent. Initial studies using T. huegelii in wastewater treatment experiments has shown that Triglochin has consistently higher concentrations of nitrogen and phosphorus than Schoenoplectus validus, an emergent commonly used for wastewater nutrient stripping, in all parts of the plant - leaves, tubers and roots. In some cases, such as in the leaves, twice as much nitrogen and one and a half times more phosphorus is assimilated in the Triglochin tissue. It is also likely that T. huegelii will remove nitrogen and phosphorus at a greater rate than many other types of aquatic macrophytes. The implication is that instead of only planting the perimeter of lagoons, artificial wetlands and constructed basins we should be planting the bulk of the waterway with submergent species such as Triglochin spp. which may be far more effective in stripping nutrients than emergents currently used for that purpose.