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Scholder’s research focuses on using red worms, which eat their own weight in biosolids every day, for vermistabilization. Photo courtesy of Scholder.

Earthworms used for vermistabilization include red worms, garden worms, and night crawlers. Each type consumes organic material, including microorganisms; crystalline minerals, such as sand, silt, and clay; and detritus, such as leaf litter. Each also lives in a different level of the soil: Red worms live in the top 102 mm (4 in.) of soil, garden worms live between 102 and 254 mm (4 and 10 in.) deep, and night crawlers live between 254 mm (10 in.) and bedrock, Scholder said.

Scholder said his work focuses on red worms, because this earthworm species consumes and processes more material than other worms. Under optimal conditions, one red worm continuously eats throughout the day and can produce four to eight additional worms every 9 weeks, he said.

“I know what worms like; I know how they like to eat,” Scholder said. According to “conservative estimates,” red worms eat their own weight in biosolids every day, and 1000 worms, or 0.45 kg (1 lb) of worms, can fit comfortably in 0.09 m2 (1 ft2) of soil, he said. Scholder also knows how to increase a red worm’s size by 20% to 30% so it can treat even more biosolids. At these rates, Scholder estimates that these worms can process 18 Mg/d (20 ton/d) of biosolids on 0.4 ha (1 ac).

“The only thing that slows [worms] down is environment,” Scholder said. “And I know all those parameters. I know the maximum efficiency of what a worm can do.” He explained that optimal living conditions for worms include a soil temperature between 21°C (70°F) and 26°C (78°F), neutral pH, and 80% moisture.

“If you give them the proper food in the proper environment … they are not going to leave,” Scholder said.

Scholder has applied his Class A vermicastings to his own yard and seen his plants’s growth increase. Photo courtesy of Scholder.

Because regulations prohibit transporting Class B biosolids from water resource reclamation facilities, Scholder’s biosolids supply has been stopped, and his worms have been eating food and vegetative waste. But experience has shown that with the proper management process, vermistabilization is a low-cost, low-maintenance, environmentally beneficial solution to treating biosolids and generating a substance that can improve soil, Scholder said.

Scholder can tell when biosolids have been processed because vermicastings resemble sand, with small and uniform grains, and no longer have an odor, he said. This indoor bin shows vermicastings. Photo courtesy of Scholder.

Scholder’s research takes place across 37 to 56 m2 (400 to 600 ft2) of his backyard, where about 181 kg (400 lb) of red worms reside. He has installed wood bins measuring 0.6 m (2 ft) deep, 1.2 m (4 ft) wide, and 3.7 m (12 ft) long in his fenced-in yard. The bins have 6-mm (0.25-in.) holes on all sides for aeration, which is important for the worms. During winter, the bins are covered with landscaping material and topped by rugs to protect the worms from low temperatures.

“I’m very, very careful about what I do, because I understand the importance of it,” Scholder said.

Wearing a mask and gloves, Scholder transported 1225 kg (2700 lb) of Class B biosolids from his local water resource reclamation facility. He made nine trips, hauling 136 kg (300 lb) of biosolids on each trip to his home. The worms completed vermistabilization of all of these solids within 10 days, Scholder said. Regulations prohibit the sale of vermicastings from biosolids, so Scholder has applied them to his yard, and the results in his garden have been impressive, with plants growing faster and taller than normal, he said.