Solid Waste & Recycling

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Municipalities face a challenge deciding what to do with sewage sludge and other types of organic waste. Some truck dewatered sludge to landfills for disposal, others incinerate it. But progressive mu...


Municipalities face a challenge deciding what to do with sewage sludge and other types of organic waste. Some truck dewatered sludge to landfills for disposal, others incinerate it. But progressive municipalities may utilize sludge beneficially.

International Bio-Recovery Corp. (IBR), a Vancouver, British Columbia-based company, has developed a technology that converts these wastes into a valuable resource. An independent research study conducted by CanTest Laboratories entitled Process Assessment for Treating Sewage Sludge confirmed the commercial viability of IBR’s system, which was developed in conjunction with the National Research Council of Canada and the University of British Columbia. Mixed organic waste is the feedstock for an enhanced autogenous thermophilic aerobic digestion (ATAD) process.

Traditionally, the differences in pH and composition of waste, oxygen and bacterial requirements made it impossible to digest mixed batches of organic material and sewage sludge. But IBR’s three-stage process efficiently transforms these materials into a marketable fertilizer.

The study

For the study, sewage from Vancouver’s Iona Treatment Facility was pumped from several tanker trucks directly into the IBR plant’s macerator. During the transfer, negative air pressure and a proprietary biofilter controlled odors. The biofilter contains active layers of odor-consuming bacteria. (Hence, the plants can be located in dense urban areas.)

The macerated slurry was then pumped into the primary digester and the pH and temperature were adjusted to optimum ranges for thermophilic digestion. (The ideal consistency for this is eight per cent solid.)

The proper temperature inoculated the sewage slurry after which time it was transferred to a secondary digester equipped with Shearators, a patented machine designed to deliver oxygen to the slurry.

Bacterial activity inside the digester increased the temperature to approximately 75C. The time-temperature regime ensured complete conversion, pathogen removal and pasteurization. Oxygen, temperature and pH are monitored and controlled at all times.

Organic materials digest at different speeds due to their physical and chemical characteristics. Some may require 72 hours of digestion, but the sewage slurry was fully digested after only 48 hours. The material was then screened through a 1/4-inch mesh and separated into solid cake (45 per cent total weight) and filtrate (1.5 per cent total weight).

Results

As indicated in Table 1, the study concluded that IBR’s system successfully treated the sewage sludge. The level of gram-negative enteric bacilli pathogens in the sludge was reduced from 3.5-billion colony forming units per gram of dry sewage to zero detectable colonies.

The research also indicates that the metal concentration present in the slurry at the start of digestion, on a dry weight basis, is similar to the concentration of heavy metals in the final product. Different mixtures of raw sewage and vegetable/food matter can lower the final metals concentration significantly below Canadian and U.S. regulated standards. (See Table 2.)

End products

The end product is a fertilizer that complies with the EPA Part 503 Biosolids Regulation. Although the plant does not currently process sewage sludge, research indicates that the process can be used for this purpose. The annual revenue of a 450 tonne/day plant (based on a $50/tonne tip fee) would be approximately $14.4-million. A plant built for $10-million would break even within three years.

The company has developed a variety of solid, pelletized organic and organic-based fertilizers manufactured from food waste available to commercial growers and consumers. Currently, IBR’s solid fertilizer product wholesales for $350 per tonne. (One product retails under the brand name Seasons. A new line called Frenz is planned for commercial release in spring 2001.)

See www.solidwastemag.com for a link to the complete study.

Ben Van Dyk is president of International Bio-Recovery Corp., based in Vancouver, British Columbia.

Table 1. IBR Results: Gram negative enteric bacilli (includes fecal coliforms)

Time Eosin Methylene Blue Agar** MacKonkey’s Agar***

(Hours) Total Possible E. Coli Total Possible Salmonella
(cfu*/g dry) (cfu/g dry) (cfu/g dry) (cfu/g dry)
0 3,530,000,000 192,000,000 484,000,000 235,000,000
14 688 0 0 0

63 0 0 0 0

*** colony forming units

*** Baterial growing media for isolating and differentiating gram-negative enteric bacilli.

*** Baterial growing media for isolating and differentiating lactose fermenting form lactose non-fermenting gram-negative enteric bacilli.

Table 2. IBR’s Heavy Metal Concentration with Canadian and U.S. Standards

Metal Agriculture Canada EPA Concentration IBR Solid Fertilizer
Max. Acceptable limits for biosolids Product (ppm)
Metal Concentration (ppm)

(ppm)

Arsenic 75 41 <

Cadmium 20 39 <

Cobalt 150 — <

Mercury 5 17 0.19

Molybdenum 20 — <

Nickel 180 420 10

Lead 500 300 25

Selenium 14 36 <

Zinc 1,850 2,800 86

< less than detection limit


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