Time filter

Source Type

Port Macquarie, Australia

Johnston S.G.,Southern Cross University of Australia | Burton E.D.,Southern Cross University of Australia | Aaso T.,Port Macquarie Hastings Council | Tuckerman G.,Great Lakes Council
Chemical Geology | Year: 2014

Freshwater re-flooding is a relatively novel approach to remediate drained acid sulfate soil (ASS) wetlands. This study documents the geochemical consequences of restoring freshwater re-flooding for contemporary reduced inorganic sulfur (RIS) and iron species in two coastal floodplain ASS wetlands. Re-flooding has established predominantly reducing/suboxic conditions and encouraged organic carbon accumulation in surface sediments (~20-30%). The pH of former sulfuric horizons has increased by ~2-3 units, partly in response to alkalinity generation from anaerobic metabolism of organic carbon coupled with Fe(III) and SO4 2- reduction. Despite considerable sulfidisation, reactive Fe (FeR; sum of 1M HCl and citrate-dithionite extracts) and non-sulfidic Fe(II) remain abundant in both wetlands. High concentrations of Fe2+ (up to ~5mM) in wetland porewaters represent a considerable pool of labile net acidity and is partly a result of insufficient S(-II) to sequester excess Fe2+. Accumulation of iron sulfides appears to be constrained more by SO4 2- and carbon availability rather than FeR. Reformation and accumulation of RIS species is greatest in organic-rich surface horizons (~40-500μmolg-1), where time integrated RIS accumulation rates approximate 10-100nmolg-1 d-1. While pyrite is the dominant RIS species to have formed since re-flooding, there is anomalous accumulation of S(0) (up to 80μmolg-1), accounting for ~50% of the RIS pool in some samples. Greigite (Fe3S4) has formed in near-surface sediments and while AVS-S is a minor component of the RIS pool overall, at some locations maximum concentrations exceed 300μmolg-1. Contemporary near-surface pyrite is characterised by abundant small (200-300nm) crystals, in contrast to relic sedimentary pyrite of estuarine origin that is dominated by larger crystals with diverse habit. Although Fe and SO4 2- reduction are partly responsible for wetland-scale recovery from acute acidification, the resultant accumulation of diverse RIS species in surficial sediments indicates an oxidative component to the S-cycle and represents a hysteresis in S-cycling that contrasts markedly with the drained conditions existing before remediation. Analysis of seasonal climate fluctuations suggests that near-surface sediments containing contemporary RIS are vulnerable to oxidation and possible temporary re-acidification during future drought episodes. This study underscores the long-term legacy of ASS wetland drainage and highlights the need for both considered hydrological management of re-flooded wetlands and further study to quantify possible re-acidification risks associated with seasonal drought. © 2014 Elsevier B.V. Source

Johnston S.G.,Southern Cross University of Australia | Burton E.D.,Southern Cross University of Australia | Hagan R.,Southern Cross University of Australia | Aaso T.,Port Macquarie Hastings Council | Tuckerman G.,Great Lakes Council
Applied Geochemistry | Year: 2015

Titratable actual acidity (TAA) is a technique commonly used to estimate the existing pool of exchangeable H+ in acid sulfate soils (ASS). A widely adopted version of the TAA method involves titrating a 1M KCl suspension of oven-dry soil (1:40) with NaOH to a known pH endpoint. However, when ASS are subject to long term re-flooding during wetland remediation, former sulfuric horizons can develop substantial quantities of porewater Fe2+, non-sulfidic solid-phase Fe(II) and a variety of reduced inorganic sulfur (RIS) species (e.g. pyrite, mackinawite, greigite and elemental sulfur). For these sediments, an oven-drying approach may induce oxidation of the abundant Fe(II) and/or reactive RIS species, thereby generating H+ and leading to overestimation of existing in situ exchangeable H+. In this study, we compare TAA via the standard approach (1M KCl; 1:40; oven-dry soil, 4 hr extract; TAAD) with an identical O2-free extraction approach using wet-sediment (TAAW). We apply both methods to former sulfuric horizon sediments from freshwater re-flooded ASS wetlands. There are significant (α=0.01) differences (up to 12×) between TAA measured by the two methods, with the oven-dried standard approach overestimating TAA relative to the wet, O2-free approach in 85% of cases. Despite the fact that all AVS-S and some S(0) was oxidised during the oven-drying process, the increases in TAA (TAAD-TAAW) show very weak correlation(s) with corresponding losses in RIS species or increases in water soluble sulfate and KCl extractable sulfate. However, oven-drying caused substantial loss of 1M KCl exchangeable Fe(II) and 1M HCl-extractable Fe(II) and led to large increases in 1M HCl-extractable Fe(III). These changes in Fe fractions displayed strong positive linear correlation (α=0.01) with increases in TAA. Although this is not evidence of causality, it suggests that oxidation of Fe(II) species are playing an important role in the development of additional exchangeable H+ and may be largely responsible for the contrasting TAA derived by the two methods. The differences in TAA between the two methods are greatest in organic-rich surface sediments and are significantly positively correlated with total organic carbon content. These findings have major implications for accurately assessing TAA in re-flooded ASS wetlands. © 2014 Elsevier Ltd. Source

Chen Z.,University of Technology, Sydney | Ngo H.H.,University of Technology, Sydney | Guo W.,University of Technology, Sydney | Wang X.C.,Xian University of Architecture and Technology | And 4 more authors.
Journal of Environmental Management | Year: 2013

Recycled water for household laundry can be regarded as a promising strategy to alleviate the current demand on scarce water supplies. Public acceptability becomes fairly important to ensure the successful establishment and development of this new end use. To address the issue, this study conducted social surveys in two locations of Australia, Port Macquarie and Melbourne, where respondents were asked 17 questions. The regression models provide conclusions about which characteristics are more likely to lead to the acceptance of recycled water from society. Three attitudinal variables (RWAlterDW, Attitude and Cost) and three psychological variables (Odour, Reading and SmallUnit) were found to be the key driving forces behind domestic water reuse behaviour. These findings could drive the future research direction to achieve better public perception of this new end use of recycled water. © 2013 Elsevier Ltd. Source

Chen Z.,University of Technology, Sydney | Ngo H.H.,University of Technology, Sydney | Guo W.,University of Technology, Sydney | Pham T.T.N.,University of Technology, Sydney | And 6 more authors.
Science of the Total Environment | Year: 2014

With a constantly growing population, water scarcity becomes the limiting factor for further social and economic growth. To achieve a partial reduction in current freshwater demands and lessen the environmental loadings, an increasing trend in the water market tends to adopt recycled water for household laundries as a new recycled water application. The installation of a small pre-treatment unit for water purification can not only further improve the recycled water quality, but also be viable to enhance the public confidence and acceptance level on recycled water consumption. Specifically, this paper describes column experiments conducted using a 550. mm length bed of zeolite media as a one-dimensional flow reactor. The results show that the zeolite filter system could be a simple low-cost pre-treatment option which is able to significantly reduce the total hardness level of recycled water via effective ion exchange. Additionally, depending on the quality of recycled water required by end users, a new by-pass controller using a three-level operation switching mechanism is introduced. This approach provides householders sufficient flexibility to respond to different levels of desired recycled water quality and increase the reliability of long-term system operation. These findings could be beneficial to the smooth implementation of new end uses and expansion of the potential recycled water market. The information could also offer sound suggestions for future research on sustainable water management and governance. © 2014 Elsevier B.V. Source

Mainali B.,University of Technology, Sydney | Pham T.T.N.,University of Technology, Sydney | Ngo H.H.,University of Technology, Sydney | Guo W.,University of Technology, Sydney | And 5 more authors.
Science of the Total Environment | Year: 2014

Laundry is a potential new end use of recycled water in dual reticulation systems. Generally, the community is willing to accept this new end use if it can meet the concerns on health issues, durability of washing machine, cloth quality and aesthetic appearance. This study addresses all these major concerns thereby assisting in the introduction and promotion of this new end use in the existing and proposed dual reticulation systems. Five representative cloth materials were selected for washing in tap water and in recycled water for up to 50 wash cycles for comparative studies. The tearing/tensile strength tests were used for the assessment of cloth durability. ANOVA one way test was applied for the significance analysis (Tukey's test p. <. 0.05) which indicated that there is no significant change in the tensile/tearing strengths of washed cloth samples. Scanning electron microscope (SEM) images of the washed cloth samples found no distinct change in surface morphology. Textile colour analysis (CIEDE2000) analysed the variation in colour of the washed cloth samples and showed that the change in colour {increment}E ranges from 0-1 revealing no visible difference in colour of cloth samples. Langelier Saturation Index (LSI) was used as the indicator for predicting corrosive/scaling potential of recycled water. The LSI values ranged from +. 0.5 to - 0.5, indicating no corrosive or scaling potential of recycled water. The microbiological study of the cloth samples washed in recycled water indicated that there was no contamination with representative bacteria. As the recycled water has similar effects like tap water on cloth and washing machine, it is safe to use for laundry. © 2013 Elsevier B.V. Source

Discover hidden collaborations