Solids that accumulate in municipal or industrial secondary treatment plants are a valuable byproduct that contain essential plant nutrients and should be used as a soil amendment to increase crop or …
Solids that accumulate in municipal or industrial secondary treatment plants are a valuable byproduct that contain essential plant nutrients and should be used as a soil amendment to increase crop or timber production, or to manufacture topsoil. Information from a recent biosolids recycling conference indicates that the industry can learn a great deal from the municipal biosolids recycling community. Here are some of the key messages from the conference that focused on re-use of biosolids. In many cases, the key is still getting people to change the way they think.
WHAT ARE BIOSOLIDS?
In many US sewage treatment plants (STP), the solids are collected and biologically stabilized in a digester by beneficial microorganisms that decompose or digest the solids. This stabilization process reduces odour and destroys most of the potentially harmful pathogens contained in the solids. These stabilized solids are mostly organic matter, rich in essential plant nutrients. Biosolids are ready to be returned to the environment as a fertilizer and soil conditioner. They can be recycled directly onto soils in the forest or on agricultural land or be composted and used for landscaping and gardening.
In the pulp and paper industry, biosolids are produced in aerated stabilization basins (removed by dredging) or activated sludge systems (waste activated sludge alone or mixed with primary clarifier solids). To be cost effective, mills should focus on producing primary and secondary solids of the highest possible quality by improving in-mill losses and optimizing primary and secondary treatment operations. The savings in effluent and solids management can be substantial and will help drive solids re-use.
BIOSOLIDS APPLICATIONS AND ADVANTAGES
When properly applied and managed, biosolids can also improve soil structure and tilth, add organic matter, enhance moisture retention, and reduce soil erosion. Municipal biosolids recycling is regulated and encouraged by many U.S and Canadian jurisdictions.
Forestry: Biosolids are recycled in forestry to grow timber for lumber and pulp wood. Where biosolids have been used, the trees grow faster than those do in unfertilized soils.
In many cases, forest soils have relatively small quantities of nutrients and organic matter, which can inhibit tree productivity. The fine particles and organic matter found in biosolids can quickly enhance soil moisture and nutrient-holding characteristics. In the long-term, biosolids provide a continual slow release of nutrients to the soil as the organic matter decomposes and site productivity may be permanently improved.
Soil improvement: Severely disturbed soils can be reclaimed through the addition of biosolids to replace lost topsoil.
Biosolids have also been used by government departments in the Northwest US to obliterate and revegetate logging roads.
Agriculture and landscaping: Biosolids provide essential plant nutrients such as nitrogen, phosphorus and zinc for healthy crops. Two factors help control soil erosion. Root growth is promoted by improving soil tilth, enhancing moisture retention, and encouraging earthworms. Biosolids can also play an important role in soil fertilization and conservation. For example, in one farm the use of biosolids has allowed to graze 350 head of cattle on 1800 acres instead of 5200 previously required.
Biosolids composted with sawdust, woodchips, yard clippings or crop residues make excellent mulches and topsoil.
Top soil blending: Blends of ash, fibre clay from primary clarifiers, wood waste, shredded paper, dredgeate from rivers, and lime mud from mills have all been used in varying proportions to “blend” top soil for eventual use in the above applications. One important item to remember is that primary pulp and paper solids (from clarifiers) is an excellent binding agent that increase the retention of nitrogen and water in soils.
Education and partnerships: The use of biosolids is well regulated in the US and Canada. Although the regulations include criteria for pathogens and many chemical parameters, there are still public concerns about biosolids use. The key issues mentioned at the conference were odour, pathogens, dioxins and furans. Several strategies were presented for better public education and information distribution.
One-day workshops with schools and teachers, including student projects.
Workshops with stakeholders (government, farming associations, municipality, industry).
Work with experts to educate people in your area.
Include the benefits of biosolids on Internet sites. Produce promotional material (i.e. video, CD) and fact sheets for distribution. Use the educational material already developed by some biosolids associations like the New England Biosolids Recycling Association (NEBRA) and the Northwest Biosolids Management Association (NBMA).
Use biosolids in noticeable public areas to show the growth benefits (i.e., city flower beds, schools).
There are over 2200 reports on biosolid re-use.
Spoil without the p = soil
We are not producing waste. It is a resource, a byproduct for re-use. Avoid the word “sludge” because sludge is perceived as “toxic waste”.
Have one-on-one discussions with potential users (i.e. farmers) to gain acceptance and run a trial to demonstrate the advantages of biosolids.
If we don’t recycle biosolids what should we do with them?
No biosolids recycling means higher disposal cost, higher energy use, reduced crop yield and reduced income for farmers.
INFORMATION SOURCES
The most relevant web sites are:
www.biosolids.org
www.nas.edu
www.agr.okstate.edu/soilchem
www.nebiosolids.org (see the “Saving Soil” report)
Anyone with an interest should join NEBRA and NBMA. The NBMA has good publications including The Forest Alternative: Principles and Practice of Residual Use.
The key is to identify a market for the product and demonstrate the environmental and economical advantages of biosolids recycling by doing a cost analysis that includes savings due to waste re-use instead of landfilling or burning. The hardest part may be “selling the idea”.P&PC
Phil can be reached at phil.riebel@upm-kymmene.com.
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