Review of biofiltration processes relevant to water reclamation via aquifers

[摘要] Executive Summary:The biological clogging of natural porous media, often in conjunction with physical or chemical clogging, is encountered during managed aquifer recharge (MAR).The biologically mediated clogging often observed in MAR applications is affected by the character and concentration of biodegradable organic matter (BOM) in source waters.Biofiltration is a water treatment technology used to reduce BOM concentrations in source waters and hence has potential to limit biologically mediated clogging in natural porous media.Futhermore, the biofiltration media may behave similarly to aquifer media, potentially allowing much more precise and simpler measurements of coincident processes of BOM uptake and removal.This could lead to an improved understanding of near well processes in aquifers where it manifests as well as clogging.Slow sand filtration (SSF), a 'low technology' form of biofiltration, is recognised as the earliest established water treatment technology for provision of safe drinking water.SSF is also recognised as a technology that is simple and robust and can readily be adopted where sufficient space is available.Applications of SSF range from provision of safe water in rural, remote, and developing communities to its integration within extensive tertiary treatment trains for achievement of specific water quality targets in high technology applications.SSF's robust character and generally simple technology highlight its potential as pretreatment for MAR, and is particularly in line with the UN Millenium goals for safe drinking water in the developing world.The design, construction, and operation of SSFs are well defined but, for safe potable water supply, are predominantly for pathogen and turbidity removal.Design features typically include the use of ~ 1m depth of sand filter media, with a uniform small grain size (~0.2 mm).An operational feature of SSF is the slow filtration rate of ~0.1 m/h which distinguishes it from much faster filtration rates of rapid gravity filters, and 5 - 30 m/h.Another defining characteristic of SSF is the formation of a schmutzdecke, a thin organic layer composed mostly of gelatinous material (micro-organisms and biofilm) in the first few centrimetres of the filter bed.The schmutzdecke supports the necessary microorganisms and macroinvertebrates that act as the primary biofiltration process in the removal of BOM, pathogenic microorganisms and particulates.Another key strength of SSF is its capacity to produce biologically stable water (or improve its stability with respect to bacterial growth, usually in the context of drinking water distribution systems).This is due to the reduction of typically ~10 - 40% of BOM [also reported variably as assimiliable organic carbon (AOC) and biodegradable organic carbon (BDOC)].In recent years the technology as been adopted as a final polishing step in treatment trains in order to achieve biologically stable influent water which should then lower the potential of biologically mediated well clogging.The capacity of conventional SSF to produce biologically stable waters from various source waters (catchment subsurface and surface runoff, wetlands, urban stormwaters)sufficiently for sustainable siliceous aquifer recharge and recovery requires investigation.In assessing the potential of SSF for MAR pretreatment applications, this review was conducted on literature reported SSF operations and performances and on the mathematical models developed to describe them.Generally modelling has been along one of three broad themes: predicting removal of key contaminants; modelling of biological growth and the formation of the schmutzdecke and the modelling of operationally significant factors such as hydraulic head loss.

[发布机构] CSIRO

[学科分类] 地球科学(综合)