USE OF PEAT FOR ON-SITE WASTEWATER-TREATMENT .1. LABORATORY EVALUATION

Peat is an effective medium for the treatment of municipal and industrial waste waters. Recent research indicated that a peat filter can be utilized in the treatment of septic tank effluent (STE). Laboratory columns were used to determine the treatment capacity of sphagnum (Sphagnum spp.) peat at varying hydraulic and organic loadings. Peat (30 cm) compacted to a density of 0.12 Mg/m3 was sufficient to treat STE at a hydraulic loading of 8.1 cm/day and an organic loading of 20.2 kg BOD3/1000 m2 per day (BOD5 = 5 day biochemical O2 demand). The BOD reduction exceeded 95% and suspended solids 90%. Chemical O2 demand (COD) reduction was only 80% as the effluent COD exceeded 100 mg/l. The relatively high COD was attributed to the organic matter leached from the peat itself. This was reflected in a lighr yellow color and lowered pH in the effluent. The effect seemed to have been temporary in nature and improved COD, color and pH values were obtained with time. Excellent fecal coliform reduction was obtained, suggesting that a separate disinfection operation was not necessary. Nutrient removal under aerobic conditions revealed < 10% P and N removal; nitrification was nearly complete. Significant denitrification was promoted under anaerobic conditions and a 62% reduction in total N was observed. Specifications for a full-scale filter included a hydraulic loading of 4.1 cm/day for a typical strength STE (10 kg BOD5/1000 m2 per day) as 8.1 cm/day proved to be excessive at low temperature (5.degree. C). The filter should have a minimum of 30 cm of lightly compacted peat (0.10-0.12 Mg/m3) below the distribution pipes. These recommended design criteria result in a smaller filter than previously tested.