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United States Department of Agriculture

Agricultural Research Service

Research Project: DEVELOPMENT OF SUSTAINABLE LAND-BASED AQUACULTURE PRODUCTION SYSTEMS

Location: Cool and Cold Water Aquaculture Research

Title: The Cost and Effectiveness of Solids Thickening Technologies for Treating Backwash and Recovering Nutrients from Intensive Aquaculture Systems

Authors
item Sharrer, Mark -
item Rishel, Kata -
item Taylor, Amanda -
item Vinci, Brian -
item Summerfelt, Steven -

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2010
Publication Date: September 1, 2010
Citation: Sharrer, M.J., Rishel, K., Taylor, A., Vinci, B.J., Summerfelt, S.T. 2010. The Cost and Effectiveness of Solids Thickening Technologies for Treating Backwash and Recovering Nutrients from Intensive Aquaculture Systems. Bioresource Technology. 101(17):6630-6641.

Interpretive Summary: Scientists at the Conservation Fund Freshwater Institute evaluated the cost and effectiveness of three solids thickening processes, i.e., gravity thickening settlers (GTS), inclined belt filters (IBF), geotextile bag filters (GBF), while treating the biosolids backwash produced in intensive aquaculture systems equipped with microscreen drum filters and radial flow settlers. Results indicate that all processes removed 94-96% of the TSS applied. The IBF produced the cleanest discharge and highest treatment efficiencies, whereas the GBF was the least effective, i.e., leaching into the GBF permeate created the highest concentrations total phosphorus, total nitrogen (primarily ammonia), and carbonaceous biochemical oxygen demand. GBF was most effective for sludge volume reduction; final solids concentrations of dewatered sludge were 22 +/- 1%, 14%, and 11 +/- 0% for the GBF, GTS, and IBF. The GTS system provided biosolids dewatering capacity and waste capture at the lowest capital and annual operating cost. In contrast, an estimate of the annual cost to operate a GBF system was orders of magnitude higher than the IBF and GTS, due to the high cost to replace geotextile bags. Capital cost estimates for an IBF system were more than twice that of GTS and GBF systems of similar treatment capacity.

Technical Abstract: The cost and effectiveness of three solids thickening processes, i.e., gravity thickening settlers (GTS), inclined belt filters (IBF), geotextile bag filters (GBF), were individually evaluated with the biosolids backwash produced in intensive aquaculture systems equipped with microscreen drum filters and radial flow settlers. Backwash flows applied to each technology assessed ranged from 0.1-0.2% total solids. The GTS was assessed with no coagulation / flocculation amendment. However, backwash flows applied to the GBF and IBF were amended with alum (50 mg/L) and polymer (25 mg/L) to maintain flow through the geotextile's approximately 425 µm openings and belt's 300 µm openings. Results indicate that all processes removed 94-96% of the TSS applied. The IBF produced the cleanest discharge and highest treatment efficiencies, whereas the GBF was the least effective, i.e., leaching into the GBF permeate created the highest concentrations total phosphorus, total nitrogen (primarily ammonia), and carbonaceous biochemical oxygen demand. Treatment across the GTS was intermediate between the IBF and GBF. However, the GTS did not require any alum or polymer to achieve this level of performance and was the least complicated process and required the least labor to maintain. Belt filter operation was more complicated and time consuming than the other processes. However, GBF was most effective for sludge volume reduction; final solids concentrations of dewatered sludge were 22 +/- 1%, 14%, and 11 +/- 0% for the GBF, GTS, and IBF. The higher nitrogen, phosphorus, potassium concentrations (i.e., retention in the biosolids) observed in the IBF biosolids cake likely reflected the rapid efficiency with which solids are separated from wastewater and the increased nutrient leaching that occurred in the GTS and GBF, which contained the lowest percentage of nutrients and potassium in the biosolids. Capital cost estimates for an IBF system were more than twice that of GTS and GBF systems of similar treatment capacity. In addition, the GTS system provides biosolids dewatering capacity and waste capture at the lowest capital and annual operating cost. In contrast, an estimate of the annual cost to operate a GBF system was orders of magnitude higher than the IBF and GTS, due to the high cost to replace geotextile bags.

Last Modified: 10/1/2014
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