Using Peat to Treat Wastewater.

The vast majority of on-site systems treat wastewater with natural soil or selected sand, whose cost, quality, and availability vary from county to county. Peat-based systems represent an interesting substitute for other natural soil systems. Also, the distribution network and the accessibility of peat in the northeast and northwest regions of the United States make it possible to implement peat systems throughout the country at an affordable price.

Where Does Peat Come From? Sphagnum peat moss is a natural organic material created in very humid conditions when plant debris, predominated by sphagnum moss, accumulates. The debris decomposes very slowly because of the absence of air in the deposit, bad drainage of the ecosystem, and acid conditions. Peat moss in its raw state is a spongy, fibrous, lightweight material whose color varies from light to dark brown depending on the degree of decomposition.

Thousands of years ago, plant matter started to pile up in old riverbeds, lakes, ponds, and glacial basins. Peat bogs now cover nearly 12 percent of the northern regions of North America, and their total surface is estimated at over 127 million hectares.

How Does Peat Treat Wastewater? Because of its porous structure, this natural resource is mainly characterized by its high liquid retention capacity. Peat can absorb up to 20 times its dry weight in water. A high organic-material content, low density, and a resistance to degradation enable peat filters to treat wastewater through a combination of physical (filtration and absorption), chemical (adsorption and ion exchange) and biological (microorganism) interactions. Since peat helps hold pollutants and support microorganisms, it makes an ideal organic filtering medium for wastewater treatment. In fact, the excellent sorption capacity means that peat can trap pollutants either permanently (in the case of heavy metals and nonbiodegradable organic substances) or long enough for biodegradation to occur (in the case of toxic but slowly biodegradable pollutants).

Because the scientific literature has identified peat as a very promising alternative onsite wastewater treatment technology some research centers have been developing simple peat-based systems similar to conventional systems. These systems produce effluent of consistently high quality: biochemical oxygen demand (BOD) and total suspended solids (TSS) are both less than 10 milligrams per liter (mg/L), and fecal-coliform counts are less than 25,000 colony-forming units (CFU) per 100 milliliters (mL). Thus, reductions of BOD, TSS, and fecal coliform are around 95 percent, 90 percent, and 99 percent, with pH close to neutral (6.5 to 7.5) after a few hours under normal operating conditions.

How Are Peat-Based Systems Managed? Peat-based biofilters use a consistent, quality-controlled filtering medium that retains its purifying capacities over time. Conventional septic systems have to be relocated after a certain number of years, but with the biofilters, only the peat filter bed has to be replaced. All this operation requires is pumping the filter bed with a standard septic vacuum truck. Because peat is a natural organic product, it is compatible with treatments of biological sludge such as land application. It also can be recycled into compost or organic fertilizer.

Many structured management systems take a preventive approach to system support. In fact, the selling price for peat-based systems sometimes includes a maintenance agreement that covers the lifespan of the filter.

The availability and reliability of peat make peat-based systems an interesting substitute for soil or sand absorption techniques. With correct use in a simple biofiltration system, yearly maintenance, and reliable after-sale service, peat systems now can be as efficient and consistent as soil in treating wastewater.

Corresponding Author: Nadine LeClerc, Premier Tech, 1 Avenue Premier, Riviere-duLoup, QC Canada G5R 6C1.