Investigation of Pathogen Reduction in Septage Using Storage Lagoons – Industry Survey and Lab Trials – 2007

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

Septage management is an essential component of an overall wastewater management program in rural parts of Ontario. While land application of untreated septage has been used in the past, current trends are toward a higher level of treatment and a ban on land application of untreated septage. This study was commissioned to investigate possibilities for using the treatment that occurs 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.

The survey of septage operators showed at least 25 operators have storage facilities for septage across the province. Given the typical volumes of these facilities and the volume estimates of their various operations, only a few would, with their current operation, have sufficient volume to achieve the anticipated required 12-week storage time to affect treatment.

Lab experiments were carried out to examine the reductions in pathogens (E.coli and salmonella) over a 24-week period. This included runs for different temperatures (4 and 25 degrees C) and for different mixtures of wastes. Little difference was seen for different waste mixtures while significant differences were seen for the different temperatures. Wastes stored at typical summer temperatures (25 degrees C) showed significant reductions in E.coli and salmonella. Although the wastes at 4 degrees C also showed reductions they were not nearly as substantial. Within 2 weeks the wastes stored at 25 degrees C were within the target levels for E.coli (established as 2 million CFU/g, TS, dw) while the wastes stored at 4 degrees C reached the target E.coli concentration within 4 weeks. Reductions to levels 2 logs below the target were observed within 12 weeks of storage for the septage stored at 25 degrees C. Septage stored at 4 degrees C took 24 weeks of storage to achieve the same goal. Salmonella, although present in the original samples, was only present in low concentrations. What little was present was gone within two weeks for the septage storage at 25 degrees C and within 8 weeks for the storage at the colder temperatures.

Although the lab trials clearly show that storage can affect treatment of septage to meet the guidelines, field trials are necessary to confirm this as a viable option. These field trials should encompass a range of operation types, storage times and weather conditions to confirm its viability.