January-February 2001

The topics in this newsletter are considered to be timely and of interest. Comments and suggestions are invited. The use of trade names in this newsletter is not an endorsement of any company or product by the Maryland Cooperative Extension, University of Maryland, College Park.
David S. Ross, Extension Agricultural Engineer

The purpose of this article is to briefly review the definition and production of biosolids. To begin with, it is important to distinguish "biosolids" from "sewage sludge." These two terms are sometimes used interchangeably, and often, "biosolids" is perceived as simply being a more appealing name for "sludge." It's easy to discount the importance of using these terms correctly and to assume that the materials being referred to have the same characteristics, no matter what we call them. Or, as William Shakespeare wrote (in Romeo and Juliet), "What's in a name? that which we call a rose by any other name would smell as sweet." In this case, the term we use does matter, because biosolids and sewage sludge are not equivalent and may not have the same properties and agronomic value. Correct use of these terms facilitates communication among parties that are involved with, or concerned about, the production, treatment, and disposal of wastewater treatment residuals.

Sewage sludge is the solid material produced at several stages of a municipal wastewater treatment facility. This includes solids (or primary sludge) that are settled out of screened and degritted wastewater during the initial stages of treatment. The solids produced during biological (or secondary) treatment are primarily made up of the microorganisms that are responsible for converting wastewater pollutants into harmless compounds. Secondary sludge bears little resemblance to the solids that were initially present in the untreated sewage. A third type of solids (tertiary sludge) is also sometimes produced through advanced wastewater treatment processes. For example, tertiary treatment is used if it is necessary to reduce the concentration of nutrients (nitrogen and/or phosphorus) in the wastewater to a very low level before it is discharged.

Biosolids are mostly organic, wastewater treatment solids that have been treated to meet federal and state regulations for beneficial use and recycling by land application or other methods. Biosolids are derived primarily from a combination of primary, secondary, and tertiary sewage sludges. Biosolids do not contain the coarse grit and screenings removed from raw wastewater during preliminary treatment steps or ash generated from incineration of sewage sludge. Another type of biosolids may be derived from domestic septage, the solid or liquid material removed from septic systems, portable toilets, and other systems that receive only domestic sewage.

What are the requirements for converting sewage sludge to biosolids? Untreated sewage sludge has a relatively low solids concentration (typically 1 to 4% dry solids). Therefore, in order to improve its handling characteristics and to reduce the volume of material that must be handled, it is generally thickened. The most commonly used thickening processes rely on either gravity, which causes the solids to settle, or on the introduction of air, which causes particles to float. If biosolids are to be applied to land in a liquid or semi-liquid state, no additional volume reduction may be required. However, if biosolids are to be applied in a more solid form, a dewatering step is required to increase the dry solids content to 15-30% or greater. Commonly used dewatering processes include filter belt pressing, centrifugation, and air drying on sand beds. Compared to biosolids, untreated sewage sludge has relatively high levels of disease-causing microorganisms (pathogens) and is decomposable (or unstable). The unstable nature of untreated sewage sludge can generate odors and makes it attractive to vectors, which are potential disease-carrying organisms such as insects, rodents, and birds. Therefore, the conversion of untreated sewage sludge to a biosolids product that can be land applied also involves treatment to reduce the pathogen levels and taking measures to reduce vector attraction. A variety of sewage sludge treatment processes reduce pathogen levels and make the sewage sludge less attractive to vectors. These sewage treatment processes are typically based on one or more of the following approaches: application of high temperature, application of chemical disinfectants, reduction of the microbial food source in sewage sludge (measured as the volatile organic content), or removal of nearly all moisture from the sludge. For example, aerobic and anaerobic digestion and composting are common methods of treating sewage sludge that reduce its volatile organic content and apply heat. In contrast, lime stabilization of sewage sludge involves the use of a chemical disinfectant (lime). Air or heat drying removes most of the moisture from sewage sludge.

In addition to the characteristics of the wastewater entering the treatment facility and the specific treatment processes used to produce sewage sludge and clean effluent, the processes used to reduce pathogen concentrations and vector attraction determine the characteristics of biosolids. However, although some properties of biosolids may vary, all biosolids that are land applied must meet strict federal and state regulations concerning pathogen and metals concentrations, and their tendency to attract vectors. The different biosolids classifications and the associated treatment and management requirements for land applied biosolids will be discussed in upcoming issues of Biological Resources Engineering TOPICS.

Jennifer G. Becker, Extension Engineer

Public and regulatory scrutiny of manure management on dairy farms has increased pressure to develop manure systems that minimize environmental impact. To achieve comprehensive nutrient management plan (CNMP) goals, the right combination of equipment and treatment systems must be selected. On March 20-22, 2001, a conference entitled "Dairy Manure Systems: Equipment and Technology" will be held in Rochester, New York, to provide an educational opportunity for dairy producers and their advisors. System designers, farm managers, industry experts, consultants, extension educators, and university experts from across the country will share their expertise at the conference, which is coordinated by NRAES, the Natural Resource, Agriculture, and Engineering Service.

The conference will focus on selection and management of technology and equipment, with an emphasis on traditional and new strategies to manage and design systems that move manure from the cow to its ultimate use with minimal impact to air and water quality. Stressing a systems approach to planning, speakers will present handling, storage, treatment, and land application options. The intended audience for the conference includes producers and farm managers and their advisors, soil and water conservation districts, nutrient management consultants, NRCS staff, cooperative extension educators, equipment distributors, university specialists, farm system designers and builders, environmental professionals, and regulatory agencies.

The Dairy Manure Systems Conference will begin at 12:30 P.M. on March 20 and adjourn at 12:30 P.M. on March 22. The program will include several farm case studies, with the goal of presenting each currently used equipment and technology option in the context of a complete dairy manure system. For each option described, speakers will be asked to review manure system goals, bedding, manure collection system, treatment, manure transport, storage, land application, fate of solids, neighbor and hydrologic constraints, costs, management, labor, maintenance, and pros and cons. On the evening of March 20, a tabletop exhibit session/reception will be held. Four concurrent discussion sessions are planned for the evening of March 21 on the following topics: manure composting systems, custom operators, innovative treatment technologies, and small farm systems.

State nutrient management continuing education credits have been applied for from Maryland and Virginia. In addition, international/regional CEUs have been applied for from the American Society of Agronomy Certified Crop Advisors Program. For an update on the status of CEU applications, contact NRAES.

The conference registration fee is $210 if postmarked on or before March 2, 2001. Registration postmarked after March 2 and for walk-ins is $270. The fee includes admission to the conference, one lunch, break refreshments, evening discussion sessions, admission to the tabletop exhibit session/reception, and a copy of the conference proceedings. Checks should be made payable to NRAES, in U.S. funds. All major credit cards are accepted.

Separate registration is being accepted for three optional events directly preceding or following the conference. The preconference workshop "Livestock Mortality Composting" will take place the morning of March 20; there is a $50 fee for registrations postmarked on or before March 2 ($70 after March 2). Also the morning of March 20, the "National Livestock Environmental Stewardship Curriculum" workshop will be offered without a fee to extension field educators and others who train livestock producers. An optional postconference workshop, the "National Agricultural Waste Management Initiative (NAWMI) - Northeast Planning Session," will run from 12:30 P.M. on March 22 through 12:00 NOON on March 23. The fee for the NAWMI planning session is $60 if received by March 2 ($75 thereafter) and includes two meals. It is not necessary to attend the Dairy Manure Systems conference to attend the optional workshops.

A free brochure includes the conference program, a registration form for the Dairy Manure Systems conference and the optional workshops, and other information. Conference information can also be found on the NRAES web site, . Registrations will be accepted by mail or - for those who wish to pay by credit card - by Internet, telephone, or fax. To register or to request copies of the conference brochure, contact NRAES, 152 Riley-Robb Hall, Ithaca, NY 14853-5701; phone (607) 255-7654; fax (607) 254-8770; or E-mail NRAES@CORNELL.EDU.

The conference will be held at the Rochester Marriott Thruway Hotel. Contact the hotel at (716) 359-1800 and mention "Dairy Manure" to get the special rate of $89 per night plus 14% tax for single or double occupancy. Two hotels within a few minutes' drive of the conference are also offering special rates for reservations made by March 2. Rooms at the Fairfield Inn Marriott may be reserved for $79 plus tax; call (716) 334-3350. The Microtel Inn - Lehigh at (716) 334-3400 is offering rooms at $42.95 plus tax.

NRAES, the Natural Resource, Agriculture, and Engineering Service, is a land grant university outreach program sponsored by fourteen universities. NRAES is focused on increasing the availability of research- and experience-based knowledge for producers and their advisors. All NRAES activities are guided by faculty from member universities.