Evaluation of nitrate and perchlorate reduction using sulfur-based autotrophic and mixotrophic denitrifying processes

The biological reduction of nitrate and perchlorate was comparatively evaluated in autotrophic and mixotrophic bioreactors using elemental sulfur and/or methanol as the energy source. The mixotrophic reactor was supplemented with methanol at CH3OH/NO3−-N ratio of 1 or 1.4. The mixotrophic reactor completely reduced perchlorate in the feed up to 1,000 μg l−1. The autotrophic reactor also showed high perchlorate reduction performance and decreased perchlorate from 1,000 μg l−1 to around 33 μg l−1. Complete reduction of 25 mg NO3−-N l−1 was achieved in both reactors, corresponding to a maximum nitrate reduction rate of 300 mg NO3−-N l−1d−1 and 400 mg NO3−-N l−1d−1 in the autotrophic and mixotrophic processes, respectively. Autotrophic denitrification caused an increase of effluent sulfate concentration, which may exceed the drinking water guideline value of 250 mg l−1. In the mixotrophic denitrification process, the effluent sulfate concentration was controlled by adjusting the C/N ratio in the influent. Mixotrophic denitrification was stimulated by 25 mg l−1 methanol addition and 53% of influent nitrate was reduced by the heterotrophic process, which decreased the effluent sulfate concentration to half of the autotrophic counterpart. Therefore, the mixotrophic process may be preferred over the autotrophic process when effluent sulfate concentration is of concern and a higher perchlorate reduction efficiency is desired.

Organic matter removal and disinfection byproduct management in South East Queensland's drinking water

Over the past several decades, much research has been carried out to understand and control the formation of disinfection byproducts (DBPs) of potential human health concern in drinking water. The majority of these studies have taken place in continental climates of North America and Europe, with less work investigating waters in tropical and subtropical climates. This study evaluated the occurrence, precursors and formation potentials of a range of DBPs across nine water treatment plants (WTPs) in South East Queensland, Australia. Average total organic nitrogen concentrations in raw and final waters were 0.35 and 0.15 mg N/L, respectively, and total organic carbon levels were 9.2 and 3.7 mg C/L in raw and final waters, respectively. DBP formation potential was lower on average in final waters of advanced compared to conventional WTPs, demonstrating the effectiveness of ozone/biological activated carbon (BAC) treatment at removing DBP precursors. While ozone on its own increased the formation potentials of chloral hydrate, halonitromethanes, and haloketones when followed by chlorination or chloramination, subsequent BAC treatment reduced the potential to produce these DBPs, except for tribromonitromethane. DBPs measured in the finished water leaving the WTPs were all below the Australian Drinking Water Guideline levels.

The indicator of risk of water contamination by nitrate-nitrogen

Drriven by changes in agricultural production practices, nitrogen (N) inputs have increased steadily on Canadian farms. An agro-environmental indicator was developed to monitor potential water pollution by N: indicator risk of water contamination by nitrate-nitrogen (IROWC-N). The indicator links the residual soil nitrogen (RSN) indicator to climate and soil conditions to assess the likelihood of N moving through the soil and out of the agricultural system. The results are assessed in terms of Nlost via leached water (Nlost) and its concentration in the leached water (Nconc), with the IROWC-N risk classes based on Nlost and Nconc criteria. The estimated amount of Nlost in Canada ranged from 5.1 kg N ha-1 in 1991 to 6.4 kg N ha-1 in 2001. Nconc values remained fairly constant during the 1981 to 1996 census years (ranging from 3.7 to 4.5 mg N L-1), but increased sharply (27%) to 5.7 mg N L-1 in 2001 as compared with 1996. During the 1981 to 2001 period, close to 80% of the Canadian farmland area remained in the very low and low IROWC-N risk classes, but over the years 18% shifted to a higher risk class. In 2001, large areas (> 1 million ha) in the high risk IROWC-N class were found in Manitoba, southern and eastern Ontario and in Quebec. Provincial averages of Nlost over 5 census years (1981, 1986, 1991, 1996 and 2001) varied from less than 5 kg N ha-1 in Alberta and Saskatchewan to more than 20 kg N ha-1 in Ontario, Quebec and the Atlantic provinces. With the exception of Manitoba, provincial Nconc values did not exceed the Canadian drinking water guideline of 10 mg NO3-N L-1. In each of the census years, British Columbia, Alberta and Saskatchewan had more than 70% of the farmland area in the very low and low risk classes for IROWC-N. In Ontario and Quebec, most of the farmland area was either in the low or in the high risk class. More than 50% of the farmland area in New Brunswick, Nova Scotia and Newfoundland was in the very low, low and moderate risk classes, whereas in Manitoba and Prince Edward Island, more than 60% of the farmland was in the moderate and higher level risk classes for IROWC-N. Overall, the 20-yr trend in risk of water contamination by N was worsening. Key words: Water contamination by nitrogen, nitrate, water quality, Soil Landscapes of Canada, Census of Agriculture

Bushfires and tank rainwater quality: A cause for concern?

In early 2003, after a prolonged drought period, extensive bushfires occurred in the east of Victoria affecting 1.5 million hectares of land. At the time, smoke and ash from bushfires, settling on roofs, contained pollutants that could potentially contaminate rainwater collected and stored in tanks for domestic use. The major concerns include polycyclic aromatic hydrocarbons (PAHs) from incomplete combustion of organic matter and arsenic from burnt copper chrome arsenate (CCA) treated wood. An increase in microbial contamination through altered nutrient levels was also hypothesised. A pilot study of 49 rainwater tank owners was undertaken in north-east Victoria. A rainwater tank sample was taken and analysed for a variety of parameters including organic compounds, microbiological indicators, metals, nutrients and physico-chemical parameters. A survey was administered concurrently. A number of results were outside the Australian Drinking Water Guideline (ADWG) values for metals and microbiological indicator organisms, but not for any tested organic compounds. PAHs and arsenic are unlikely to be elevated in rainwater tanks as a result of bushfires, but cadmium may be of concern.

Groundwater delivery rate of nitrate and predicted change in nitrate concentration in Blue Lake, South Australia

Blue Lake, the principal water supply for the City of Mount Gambier (South Australia), is contaminated with nitrate (NO3–) from polluted groundwater. Using existing data, a study was undertaken to determine the past load of NO3– from groundwater entering the lake and to forecast future trends in lake NO3– concentration. Groundwater NO3– loads for the 1971–1997 period were estimated with an inverse model, which combined the long-term record for NO3– concentration in the lake with a simple NO3– mass-balance. Model results show that the load of NO3– from groundwater (18–24 metric tons (t) year–1 as N) was by far the largest source to Blue Lake between 1971 and 1997. Sinks for NO3– included pumping withdrawal (10–14 t year–1), in-lake consumption (7–10 t year–1), and groundwater outflow (0–1.8 t year–1). The NO3– concentration in incoming groundwater (4–7 mg N L–1) appears to have increased slowly but steadily during the 1971–1997 period (at a rate varying between 0.037 and 0.070 mg N L–1 year–1). By assuming that the rate of increase in groundwater NO3– concentration will remain constant, a forecast for lakewater NO3– concentration was made for the 1998–2028 period. Lakewater NO3– concentration should increase from the contemporary ~3.5 mg N L–1 to 4 or 5 mg N L–1 by 2028. In the short term (decades), the rate of pumping withdrawal will be the main determinant of NO3– concentration in the lake through its impact on the rate of groundwater inflow and the lake water residence time. Although the drinking water guideline for NO3– (11. 3 mg N L–1) may not be exceeded in the short term (decades), it may be exceeded in the longer term (centuries) as NO3– concentration in the neighbouring aquifer adjusts to the contemporary land use.

Water Table Management Reduces Tile Nitrate Loss in Continuous Corn and in a Soybean-Corn Rotation

Water table management systems can be designed to alleviate soil water excesses and deficits, as well as reduce nitrate leaching losses in tile discharge. With this in mind, a standard tile drainage (DR) system was compared over 8 years (1991 to 1999) to a controlled tile drainage/subirrigation (CDS) system on a low-slope (0.05 to 0.1%) Brookston clay loam soil (Typic Argiaquoll) in southwestern Ontario, Canada. In the CDS system, tile discharge was controlled to prevent excessive drainage, and water was pumped back up the tile lines (subirrigation) to replenish the crop root zone during water deficit periods. In the first phase of the study (1991 to 1994), continuous corn (Zea mays, L.) was grown with annual nitrogen (N) fertilizer inputs as per local soil test recommendations. In the second phase (1995 to 1999), a soybean (Glycine max L., Merr.)-corn rotation was used with N fertilizer added only during the two corn years. In Phase 1 when continuous corn was grown, CDS reduced total tile discharge by 26% and total nitrate loss in tile discharge by 55%, compared to DR. In addition, the 4-year flow weighted mean (FWM) nitrate concentration in tile discharge exceeded the Canadian drinking water guideline (10 mg N l–1) under DR (11.4 mg N l–1), but not under CDS (7.0 mg N l–1). In Phase 2 during the soybean-corn rotation, CDS reduced total tile discharge by 38% and total nitrate loss in tile discharge by 66%, relative to DR. The 4-year FWM nitrate concentration during Phase 2 in tile discharge was below the drinking water guideline for both DR (7.3 mg N l–1) and CDS (4.0 mg N l–1). During both phases of the experiment, the CDS treatment caused only minor increases in nitrate loss in surface runoff relative to DR. Hence CDS decreased FWM nitrate concentrations, total drainage water loss, and total nitrate loss in tile discharge relative to DR. In addition, soybean-corn rotation reduced FWM nitrate concentrations and total nitrate loss in tile discharge relative to continuous corn. CDS and crop rotations with reduced N fertilizer inputs can thus improve the quality of tile discharge water substantially.