Thirty years ago, many American cities dumped their raw sewage directly into our rivers, lakes and bays. Today, mainly due to improved wastewater treatment, our nation's waterways have been cleaned up and made safer. Because of strict Federal and state regulations and the new innovative technology of wastewater systems, the wastewater effluent has become cleaner and cleaner. However, in the process of producing clean effluent, the process itself generates residues or solids, known as biosolids. The older, commonly used term for these solids is sewage sludge.
Biosolids are nutrient-rich organic materials produced from the treatment of domestic sewage in a treatment facility. Biosolids are carefully treated and monitored. They also must be used in accordance with strict government regulatory requirements.
After treatment and processing, biosolids can be recycled. Biosolids can be recycled in three ways: as a fertilizer, incinerate it or bury it in a landfill. Biosolids that are to be land applied must meet strict regulations and quality standards contained in 40 CFR Part 503. The Part 503 rule governing the use and disposal of biosolids contain numerical limits, for metals in biosolids, pathogen reduction standards, site restriction, crop harvesting restrictions and monitoring, record keeping and reporting requirements for land applied biosolids as well as similar requirements for biosolids that are surface disposed or incinerated. Here at the Arcadia Wastewater Utility, our biosolids meets the strict standards and can be land applied as a fertilizer.
Biosolids are an excellent fertilizer which reduces the need for chemical fertilizers. They are used to improve and maintain productive soils and stimulate plant growth. Biosolids, that have met strict quality criteria and application rates, used to fertilize fields for raising crops have been shown to produce significant improvements in crop growth and yield. Nutrients found in biosolids, such as nitrogen, phosphorus and potassium and trace elements such as calcium, copper, iron, magnesium, manganese, sulfur and zinc are necessary for crop production and growth. Biosolids are not just good for growing crops, they have been found to promote rapid timer growth, allowing quicker and more efficient harvest. Biosolids have also been used successfully in mine site reclamation to establish sustainable vegetation.
In Wisconsin, most municipal facilities apply their wastewater treatment biosolids on agricultural land as a soil conditioner or fertilizer. Biosolids applied to farmland or distributed for individual use as an exceptional quality product are produced from approximately 98% of Wisconsin's permitted municipal facilities. In 2012, 213 wastewater treatment facilities disposed of solids: 208 of these facilities either reused the biosolids or hauled them to a facility that reused them, one incinerated the biosolids and four disposed of the material by only disposing into a licensed landfill. In addition to these facilities that dispose of biosolids annually, there are 375 permitted facilities, like Arcadia, which treat wastewater in lagoon systems or other systems which only require removal of biosolids (sludge) on an infrequent basis (10-20 year cycles).
Reed Beds - An Alternative Method for Biosolids Dewatering and Storage
One of the most critical issues facing wastewater treatment facilities is the proper use and disposal of biosolids. Constructed wetland technology such as reed beds provide a long term solution by providing storage and volume reduction. Reed bed technology was first developed in Germany and is widely used for sewage sludge dewatering and stabilization in Europe, Asia and Australia. It was first introduced in the United States in the early 1980's.
In 2011, the Arcadia Wastewater Treatment Facility began construction of a Reed Bed System. This new innovative and alternative constructed wetland technology uses common reeds to break down biosolids. Reed beds are a planted biosolids drying bed. Reed bed technology features a low cost construction costs and minimal day to day operation and maintenance costs.
The reed bed system consists of concrete side walls lined with a PVC liner planted with phragmite reeds. Waste biosolids are applied periodically to the beds by simply pumping to the selected bed. The biosolids are then dewatered (the process of removing water from biosolids) through a combination of infiltration and evapotranspiration (loss of water from the soil both by evaporation from the soil and by transpiration from the leaves of the plants growing in it). The roots of the reeds create channels for the water to follow as it drains through the sand media and is returned to the lagoon for further treatment. The reeds have a high demand for water and help dry out the biosolids. The dry solids that remain in the bed accumulate over time. The beds are designed for a dried biosolids thickness of 4 feet which equals about 7-10 years worth of biosolids applications.
Sources:
United States Environmental Protection Agency (EPA)
Wisconsin Department of Natural Resources (DNR)
www.tpomag.com
www.lagoonsonline.com/reedbeds.htm
Constructed Wetlands Group