The influence of algal biomass on tracer experiments in maturation ponds

Tracer experiments are of concern to wastewater treatment engineers and researchers because of the importance of determining hydraulic regimes and retention times in wastewater treatment units. In this work, a pilot-scale maturation waste stabilisation pond (WSP) was spiked with Rhodamine WT, in order to determine how suspended organic matter would interfere with its performance as a tracer in a domestic wastewater treatment unit which had a high content of suspended algal biomass. A primary maturation pond was spiked in three separate runs with different levels of algae (high, medium and low), with a known amount of Rhodamine WT (20% v/v); the tracer was measured in the pond effluent in real time every 20 min for 3θ (the theoretical retention time, θ = 17 d). Algal biomass was monitored weekly from influent, column and effluent water samples by chlorophyll-a determination. The results show that algal biomass has a strong influence on the behaviour of Rhodamine WT as a tracer and therefore the hydraulic characteristicsm calculated from tracer curves may be affected by tracer adsorption on suspended organic matter.