Traditional methods of treating wastewater – such as an activated sludge plant – have been refined over time to become very effective. A typical activated sludge plant will include screening, sedimentation, aeration, clarification, disinfection, and sludge processing. Correctly size and situate the tanks, and the regulatory authority will have no problem approving the design. If operated correctly, the plant’s effluent will meet BOD and TSS permit limits. However, what’s to say that the “proven” methods are the only options? For those who like to think outside the box, one interesting technology that might be worth considering is the use of earthworms and microbes to treat wastewater.

The earthworm treatment process was developed in Chile in the 1990s. The system consists of boxes containing layers of geotextiles, rock, and wood shavings infused with a mix of worms and microbes. Earthworms continuously burrow channels, providing passive aeration, while also digesting large solids and depositing them into their microbe-rich casings. The nutrient-rich worm casings will eventually be removed for use as compost, and fresh wood shavings will be added. An automated system continuously irrigates the wastewater over the mixture to ensure that an optimal moisture content is maintained (optimal living conditions for worms are a soil temperature between 70°F and 78°F, neutral pH, and 80% moisture). Industry types for which this technology has been used include food processing, slaughterhouses, wineries, aquaculture, and dairies. It has also been used to treat sanitary wastewater.

One interesting case study highlighting the use of this technology is the Fezter Vineyards in Hopland, California. The typical treatment process for a vineyard would be an aeration pond. The earthworm process requires a footprint similar in size to an aeration pond but will use a fraction of the energy. At the Fetzer Vineyards, the system is expected to reduce energy consumption by 1 million kWh per year. The system will consist of three large open-top concrete boxes, each 36 feet wide by 200 feet long by 6 feet deep, with a mix of worms and microbes that match the vineyard’s waste profile. A key selling point of the system is that the entire treatment process takes 4 hours, after which the wastewater will reportedly be safe for irrigation and other non-potable uses. In contrast, a typical aeration pond might require 5 to 90 days to complete the treatment process.

William Shane is an Environmental Engineer at Smith Management Group. William can be reached at williams@smithmanage.com.