What Are Biosolids?

The wastewater industry has embarked on a significant new mission. It intends to make common the usage of a brand-new word in the English language--BIOSOLIDS. The word "biosolids" is intended to replace the term "sewage sludge" to denote the organic and nutrient rich by-product of the wastewater treatment process, a by-product which can be recycled as a fertilizer or soil conditioner.

Biosolids is a good material for soil improvement. The organic matter and nutrients replenish the soil, which is a benefit to the environment. Scientists have investigated biosolids recycling and have determined that biosolids recycling is a sound program. The potential for adverse effects from biosolids recycling is negligible. What is more, the quality of the biosolids applied to lands has greatly improved over the past decade. Today, PWD and most wastewater facilities are committed to making a biosolids product which is of far better quality than federal standards. And this is because of the wastewater industry's commitment to effective control of industrial discharges and to a high level of processing.

The Philadelphia Water Department's "Biosolids Utilization Section" is responsible for arranging the disposition of all of the collected biosolids from a regional wastewater system serving 2.3 million people. Philadelphia's program is focused on the manufacture of a special product, a fertile compost which employs biosolids as its principal ingredient, but which retains none of the odorous, unsightly or microbiological qualities that might make biosolids alone unappealing. Philadelphia today enjoys a wastewater industry reputation for having one of the most successful, large-city biosolids recycling programs.

Biosolids are classified in the Pennsylvania's Solid Waste Management Act and implementing regulations as a municipal solid waste. Despite not enjoying the favorable designation as a "recyclable" municipal waste, biosolids produced in Philadelphia have nevertheless achieved a very high recycling rate (65%). The fertility of thousands of acres of lands in the Philadelphia metropolitan area and westward has been improved with biosolids. These lands include stripmines in western Pennsylvania, farms in Pennsylvania and Maryland, sand and gravel pits in southern New Jersey, hundreds of residential and commercial properties in the suburbs, and dozens of play fields in the City.

The Water Department has continued to pursue two important recycling goals. An increasing proportion of the biosolids has been processed in a manner to make it desirable in the commercial market as a product to replace peat moss, mulch and topsoil, and the recent successful concession bid for its marketing attests to the potential for this market to grow. Secondly, the Water Department has been extremely successful at practicing "source reduction." New processing equipment and more efficient plant operations has enable the Water Department to reduce the total quantity of biosolids requiring disposition (by approximately 40% since 1992), while simultaneously improving effluent quality at the three wastewater plants.

The "showcase" biosolids product is traded as EarthMate a fine-textured, nutrient-rich, dark compost especially well suited for the establishment of turf in disturbed soils common to construction sites. Production of EarthMate constitutes one-third of all biosolids handled by the Water Department.

The Water Department recommends that EarthMate be specified as an alternative to topsoil in all city public works contracts, which have a landscape improvement component. Sample specifications are available from the Biosolids Utilization Section, and the staff agronomists are available to assist with the drafting of language tailored for special circumstances. Depending on the scope of work and availability of product, the Water Department may be able to deliver the product free-of-charge to project sites. Its performance has been well tested throughout the metropolitan area, and references are available.

For the convenience of Philadelphia residences, EarthMate is available at a Courtesy Bin at the Biosolids Recycling Center, which is open year-round.