Sludge accumulation in an anaerobic pond and viability of helminth eggs: a case study in Burkina Faso.

Accumulation rates and pathogen concentrations in primary stabilization pond sludges in developing countries are important parameters for adequate sludge management and the safeguarding of public health with sludge reuse in agriculture. An anaerobic pond has been investigated for sludge accumulation rates and helminth egg viability after four years of operation in Burkina Faso. The rate of sludge accumulation was measured at 0.037 m(3)/capita-year or 2.26 kg dry weight/capita-year. An equation describing vertical distribution of total solids in the accumulated sludge was found to be adequately represented by a regression equation. Influent helminth egg concentrations were reduced on average by 90% in the anaerobic pond effluent. Ascaris lumbricoides and Ancylostoma sp. were the most common eggs present in the sludge after four years of operation. The average concentration of helminth eggs in pond sludge was 536 eggs/g TS, and the percentages of viability ranged from 10.8% (47 viable eggs/g TS) to 57.2 (1,772 viable eggs/g TS, with an average rate of 36% (336 viable eggs/g TS). From a sludge depth and section study, egg viability was found to be randomly distributed in the sludge layer.