AWWA WQTC62441

The use of ferric or alum coagulants during drinking water treatment results in a largequantity of wet residuals. Common solutions to handle these residuals are either to directthe wet residuals to a wastewater treatment plant through a sewer connection, or to treatthem on-site to reduce the water content, and subsequently directing the residual solids toa municipal landfill. In the latter case, tipping fees can represent a significant cost to theutility. As well, new disposal regulations in the province of Nova Scotia will prevent thedisposal of alum residuals at municipal landfill sites beyond 2005. Although thediversion from landfills is a specific policy to Nova Scotia, it is an approach thataddresses long-term sustainability.Ferric coagulation plants are generally located in the United States, while alumcoagulation plants are located in both Canada and the United States. Residual availabilityspans the continent, and residuals are abundant at most plants. Due to limited disposaloptions, reuse is seen as a beneficial option. Previous research has shown that wetsolids had a sorption capacity for phosphorus in jar tests with municipal wastewater.The cost-benefit of this approach is often questionable as the wet solids have providedonly a mild benefit for phosphorus removal and the associated transportation/pumpingcosts can be prohibitive for some utilities. Research has also shown that air dried residualsolids are capable of adsorbing phosphorus from P-spiked deionized water under avariety of pH levels. The goal of this research is to examine oven dried residualsolids as an adsorbent for phosphorus removal, where oven drying has the added benefitof increasing the surface area to volume ratio of available adsorbent and significantlyreduce the residual solids volume for handling.Residual solids were collected from four water utilities located in the U.S. and Canada(Plant 1 to Plant 4). The residuals were either picked up from the plant or sent viaovernight courier. Residual solids were received at Dalhousie University as wet residual(typically 10-30 % solids). Solids were oven dried at 105ºC and stored in a desiccator.The residuals from the four plants were selected on the basis of their diversity. Plant 1uses ferric sulphate as a coagulant, whereas the other three utilities use alum-basedcoagulants. Among the alum-based plants, Plant 2 lime softens and has highconcentration of CaCO₃ in their dried solids. In contrast, Plant 3 has a raw wateralkalinity of 150-200 mg/L whereas Plant 4 has an alkalinity of less than 5 mg/L. Thusthis research will be able to compare the impact of alkalinity and coagulant type, usingthe results of the batch adsorption experiments and an analysis of the residual solidchemistry.Batch adsorption experiments were conducted in three phases:batch adsorption experiments with P-spiked deionized water to determine optimalpH level and particle sizes using alum-based residuals;batch adsorption experiments with buffered deionized water using the idealconditions determined in Phase 1; and,batch adsorption experiments with municipal wastewater effluent and the idealconditions determined in Phase 1. Includes 9 references.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

5

File Size:

1 file , 130 KB