Dissolved organic carbon (DOC) and nutrient removal from catchments using biochars as sorbents. Stage 1. Laboratory investigation.

[摘要] A range of contaminants (nutrients, pesticides, carbon, sediment and pathogens) enter waterways throughout the Mt Lofty Ranges from a diverse range of land uses.Dissolved organic carbon (DOC) in streams and the Myponga River that drain into the Myponga Reservoir continually cause problems for reservoir management including taste, odour and colour problems, the production of disinfection by-products and the promotion of biofilm growth. Various treatment processes are currently employed in the Water Treatment Plants to treat these contaminants including flocculation, filtration and chlorination.In this catchment the DOC sorption capacity of the soils and vegetation was found to have a large influence on the nature of DOC in the streams draining in to the reservoir. Minimising the off-site transport of contaminants from agricultural catchments (i.e. dealing with contaminants at their source) would assist in decreasing treatment costs in reservoirs and assist SA Water in complying with water quality standards.On-farm practices, such as buffer strips, and in-stream practices, such as sedimentation ponds, are effective strategies for decreasing the off-site transport of sediment and contaminants associated with sediment.However, contaminants that move predominately in the dissolved phase are less likely to be mitigated by these strategies.One proposed mitigation strategy is the use of biochar to remove these contaminants from water. Biochar is charred organic matter produced in solid form by dry carbonization, pyrolysis or gasification of biomass, with pyrolysis being the most common method.While the surface area of most biochar is not as high as activated carbon there are a large number of oxygenated groups, such as carboxyl, hydroxyl, and phenolic surface function groups, on the surface.These oxygenated groups have proven to be binding sites for soil contaminants. Biochar produced at temperatures above 400oC has higher surface area and this property, along with microporosity, makes them effective for removal of contaminants from water.In addition surface functional groups of biochars are important for the removal efficiency of contaminants from water. A recent review of literature showed that some biochars may be as effective as activated carbons in removing some contaminants such as pesticides. This study investigated a range of biochar materials produced from different biomass products and at different temperatures for the removal of DOC, nitrate and phosphate from solution.The sorbent materials assessed in this study (16 biochars, 2 mining by-products and 2 sands coated with chitosan) were originally collated for the National Initiative for Biochar Research or were specifically prepared for this project.Two mining by-products were also included in the assessment.The biochars were produced from a range of biomass materials including oil mallee, grape marc, rice husks and wheat straw and at a range of production temperatures.The study highlighted that for the range of contaminants considered no one sorbent material was able to remove sufficient quantities of all of the contaminants from solution.Furthermore, biochars varied widely in the amount of chemical they were able to remove and also release into solution. However, some sorbents (e.g. rice husk chars) could remove both DOC and a range of pesticides. The activated sawdust (B34) was the most effective biochar for the removal of total DOC (92%) and low molecular weight, hydrophilic fraction (1000 Da) of DOC (94%), which is difficult to treat by metal coagulation.It also had the lowest amount of DOC (8%) desorbed after the initial sorption from the Myponga River water.Of the untreated biochar materials, the rice husk materials (B29 and B43) showed promise with the removal of 47-53% of the total DOC but, more importantly for reservoir management, the removal of 71-73% of the low molecular weight, hydrophilic fraction (1000 Da) of DOC.

[发布日期] 2017-05-18 [发布机构] CSIRO

[学科分类] 地球科学(综合)