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Biosolids Technical Bulletin

This bulletin is a "must have" for anyone involved in residuals and biosolids management. Whether you're interested in the latest treatment processes, odor management, beneficial use options, environmental management systems, or public outreach approaches, this publication has the information you need.  

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Volume 17, Number 6 
November/December 2011 


Very beneficial use

Survey shows that biosolids composting remains a valuable management option 

Ned Beecher and Nora Goldstein 

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    Although biosolids composting can be a space-, labor-, and management-intensive process, it has numerous benefits. To begin with, biosolids composting saves landfill space and creates local jobs. The material produced is suitable for many applications, including agriculture, horticulture, silviculture, landscaping, site restoration, erosion control, reforestation, wetlands restoration, and habitat revitalization.  

    Biosolids compost is a vehicle for nutrients and organic matter that enriches the soil and makes plants healthier, thereby suppressing plant diseases and pests. This reduces the need for pesticides, fungicides, and chemical fertilizers. Biosolids compost also can increase crop yields and improve the crop’s nutritional value (micronutrients). In addition, biosolids compost improves the soil’s water retention, reducing irrigation needs (soil that is 30% compost can store 254 L/m3 [1.9 gal/ft3] more water than soil without compost).

    Biosolids compost can cost-effectively remediate contaminated soils via biological decomposition. It costs at least 50% less than conventional soil, water, and air pollution remediation technologies. It can remove solids, oil, grease, and heavy metals from stormwater runoff. It captures and destroys 99% of industrial volatile organic chemicals in contaminated air. It also helps reduce greenhouse gas emissions by replacing chemical fertilizers and peat, as well as sequestering carbon in soil.

    Given all of these advantages, staff at BioCycle and North East Biosolids and Residuals Association (NEBRA; Tanworth, N.H.) wanted to find out how widespread biosolids composting is. So, in 2010 they worked together to conduct a nationwide survey of this practice in the United States. 

A careful balance 

A California plant aims to boost biogas production without violating emission limits 

Jon Hanlon and Joerg Blischke

            Co-digesting fats, oils, and grease (FOG) at wastewater treatment plants has become an attractive method for boosting a plant’s renewable energy production due to FOG’s easy digestibility, high gas yield potential, and cost savings (offsetting the plant’s internal energy requirements). In addition, accepting FOG and collecting tip/disposal fees provides a source of revenue to offset the initial capital investment.

            Because each treatment plant and its service area is unique, FOG co-digestion approaches may vary greatly from municipality to municipally. Consequently, the City of Santa Barbara (Calif.) Public Works Department is undertaking a pilot study to determine how to maximize its FOG program’s financial and environmental benefits while minimizing expenses.

Solids dryers  

Lowering both operating costs and greenhouse gas emissions 

Markus Roediger

            Rising fuel and transportation costs are making biosolids disposal ever more difficult and expensive. Europe no longer permits biosolids to be landfilled because of unavoidable methane and carbon dioxide, and leachate emissions, not to mention a desire to avoid burdening future generations with long-term landfill care. It is only a matter of time before the United States follows suit.

            Incinerating solids is energy-intensive, and hauling dewatered solids to incineration sites is becoming ever more expensive. Also, landfilling the remaining ash is a waste of valuable nutrients. Global sources of fertilizer-quality phosphorus are limited, but recovering phosphorus from ash was not cost-effective at the time this was written. Phosphorus-rich ash usually cannot be land-applied because of its heavy metals content, but it could be stored in dedicated landfills, permitting future phosphorus recovery.

            Land application is under continuous threat. In some European countries, such as the Netherlands and Scandinavia, pollutant limits are so low that land application has become virtually impossible. In the United States, more and more areas prefer the beneficial use of Class A biosolids to land-applying Class B biosolids. Even where land application remains feasible, hauling distances and costs are continuously rising.

    Hauling dewatered biosolids long distances makes little economic sense. However, drying dewatered biosolids to increase the dry solids content from 25% to 90%, for example, reduces their mass by roughly 70%. Dried biosolids have a caloric value similar to that of brown coal and can be used as a carbon-dioxide-neutral and renewable fuel to produce power and heat. More and more solids dryers are being installed in Europe, the United States, and China, as well as other regions. This article will examine the features of biosolids dryers, including their benefits and disadvantages.



Land application tool quickly assesses pathogen risks 

Spreadsheet streamlines the process of estimating, addressing health risks from land application 

    A new modeling tool developed by researchers at Drexel University (Philadelphia) and funded by the Water Environment Research Foundation (WERF; Alexandria, Va.) is designed to facilitate better assessments of potential health risks related to land application of biosolids.

    By incorporating the most current data regarding microbial risks associated with biosolids, the model — known as the Spreadsheet Microbial Assessment of Risk: Tool for Biosolids, or SMART Biosolids — enables users to assess health risks as accurately as possible and determine whether changes in application practices might reduce such risks further.




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