FIELD-SCALE EVALUATION OF NATURAL WASTEWATER TREATMENT ALTERNATIVES FOR SMALL APPLICATIONS

摘要

The objective of this research was to evaluate and compare several natural treatmentrnalternatives in a real, variable, cold climate operating scenario. The treatmentrnalternatives examined include a sphagnum peat moss filter, a sand filter, a subsurfacernflow constructed wetland cell, a peat filter combined with a wetland cell, and a sandrnfilter combined with a wetland cell. These simple, passive systems provide practicalrnalternatives for on-site or small communal users because of their ability to toleraternvariable wastewater strength and flows expected with small users, operate in variablernclimates and provide high treatment efficiencies for a large group of parametersrnwithout power, chemicals, or complex operation and maintenance.rnThe project is located at the Rideau Valley Conservation Authority Workshop in Kars,rnOntario. The sampling and analysis were carried out over a period of 17 months. Thernmonitoring focused on assessing the treatment efficiency of a wide range ofrnanalytical parameters at each stage of treatment. The data were analyzed for trendsrnand used to establish predictive models that can be used to define treatmentrnexpectations for similar systems in a comparable environment.rnThe alternatives investigated showed a range of treatment effectiveness for criticalrndischarge parameters including oxygen demand, nitrogen and phosphorusrncompounds, suspended solids, and pathogenic bacteria. The sand filter has thernpotential to provide a high level of treatment for all parameters with the exception ofrnnitrate nitrogen. The peat filter provides more consistent bacterial removal andrnnitrogen reduction than the sand filter, although phosphorus reduction was lessrneffective. The wetland cell provided low to moderate treatment efficiencies for allrnparameters monitored. In combination with the filters, the wetland cells providedrnadditional reductions of the parameters monitored. The combination of the aerobicrnfilters followed by the low oxygen, high carbon wetland environment also providesrnimproved conditions for total nitrogen reduction through nitrification/denitrification.rnThe choice of treatment configuration will depend on consideration of the benefits andrnlimitations in conjunction with site specific requirements and discharge criteria.