Field Testing of Pathogen Reduction Rates in Septage Storage Lagoons – 2010

Lead Researcher: Doug Joy –
Prepared for: Ontario Ministry of Environment
Partners: Ontario Association of Sewage Industry Services

The Ontario Rural Wastewater Centre was contracted by the MOE to investigate possibilities for using the treatment that may occur during storage of septage in lagoons as a viable means of treating septage. This included investigating the numbers, sizes and types of lagoons used for septage across the province as well as lab trials to investigate the effectiveness of the storage for treatment under different temperature conditions and different mixtures of septage from septic and holding tanks. This particular study focused on field trials and was commissioned following a successful study of septage stabilization under laboratory conditions.

Three field trials were carried out to examine the reductions in pathogens (i.e. E.coli) in the fall, winter and summer periods. The trial periods lasted from 46 to 113 days and tried to capture the dynamic and static phases of operation at a typical storage lagoon facility in Ontario. The characteristics of both the raw and stored septage for all trials were found to be consistent with previously reported values of typical septic and holding tank septage in Ontario.

Results from field trials most closely resemble the lab trials conducted at 4 degrees C which were meant to represent winter conditions. Modest to no reductions in bacterial concentrations were found in the trials with only a dynamic phase while the winter trial with both static and dynamic phases achieved a reduction in terms of CFU/g TS of 0.5 to 1 log. Most of this reduction occurred in the later part of the trial during the static phase. The trials with low to no reductions in E.coli concentrations were those which had shorter durations (65 days or less), only a dynamic phase, conducted in warmer times of the year and started with higher strength waste.

Given the experience in the lab from the previous work, the lack of reduction in bacterial concentrations is less likely due to strength of the incoming wastesand more likely due to the strictly dynamic nature of the trial, the duration of the trial and the operational requirements of the particular lagoon. While recognising the results here are for only three trials, septage storage has shown to be a possible means of providing modest bacterial reductions in septage and meeting the proposed target of 2×106 CFU/100 mL. However, operational practices (such as length of storage time and the ability to incorporate both dynamic and static phases) need to considered and studied more in depth before establishing this as an effective method to reduce bacterial levels in septage.