WAS Pretreatment for Enhanced Volatile Solids Reduction and Biogas Production in Anaerobic Digestion
Authors:
- J. Hunter Long and C. Michael Bullard - Hazen and Sawyer
Stabilized biosolids from the wastewater treatment process have three primary disposal alternatives; land application, landfilling, and incineration.
Tightening regulations and reduced landfill and land application capacity have led to increasing cost of biosolids disposal. Additionally, lower nitrogen effluent limits are increasing the required liquid treatment activated sludge age which leads to a decrease in activated sludge degradability and an increase in biosolids.
In response to the rise in biosolids disposal cost an increasing number of wastewater treatment plants are evaluating sludge minimization technologies. Three biosolids minimization options are; minimizing activated sludge production by targeting the activated sludge process, increasing the bioavailability and degradability of waste activated sludge (WAS) through anaerobic digestion pretreatment, or enhanced anaerobic digestion such as temperature phased, thermophilic, or acid/gas phase digestion.
WAS pretreatment may be the alternative of choice for many wastewater treatment plants because WAS systems may be retrofitted to the anaerobic digestion process with minimal change or interruption to the overall plant process. During the past decade a number of WAS pretreatment technologies have been developed and have been shown to increase volatile solids destruction, increase biogas production, decrease the mass of stabilized biosolids, and increase the capacity of the anaerobic treatment process.
WAS pretreatment technology has gained wider implementation throughout Europe, however recent full scale tests have shown positive results at wastewater treatment plants within the United States and it is expected that WAS pretreatment will see increased implementation in the United States over the coming years. This paper provides a critical review of existing and developing technologies for WAS pretreatment and will provide a summary of data from laboratory, pilot, and full scale operations.
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