A MULTI-OBJECTIVE OPTIMISATION MODEL FOR PROCESSING AND DISTRIBUTING BIOSOLIDS TO REUSE FIELDS
Prawat Sahakij1, Mark Ramirez2, Chris Peot2, and Steven Gabriel1
1University of Maryland, USA, 2District of Columbia Water and Sewer Authority, USA
(free)
A multi-objective optimisation model to simultaneously minimise biosolids odours as well as
biosolids processing and distribution costs has been developed. We demonstrate the use of
the model with a case study for the advanced wastewater treatment plant (AWTP) operated
by the District of Columbia Water and Sewer Authority (DCWASA) at Blue Plains, in
Washington, DC, USA. DCWASA treats more than 370 million gallons per day of raw sewage
and generates over 1,200 wet tons of biosolids each day.
These biosolids are carefully regulated by environmental legislation to protect human health
and the environment and recycled as land applied fertilizer on over 700 agricultural fields
each year. Since nuisance odours from biosolids can drift into neighbouring communities,
these communities may enact legislation to ban the recycling of biosolids on nearby farm
land, and thereby jeopardize the continuation of biosolids recycling programs. In this case
study, we find several tradeoff points between costs and odours where different treatments
(e.g. lime addition) and biosolids distributions (e.g. to what reuse fields biosolids should be
applied) strategies must be employed in order to maximize the cost-efficiency of the biosolids
recycling program. In addition, to hedge the risk of equipment failures, the on-site contractor
providing additional dewatering equipments has also been incorporated into the model. This
optimisation model can be used proactively by management at wastewater treatment plants
to produce the least malodorous biosolids at minimal costs.
KEY WORDS
Biosolids odours, cost benefit, multi-objective optimisation
