The use of ferric or alum coagulants during drinking water treatment results in a large
quantity of wet residuals. Common solutions to handle these residuals are either to direct
the wet residuals to a wastewater treatment plant through a sewer connection, or to treat
them on-site to reduce the water content, and subsequently directing the residual solids to
a municipal landfill. In the latter case, tipping fees can represent a significant cost to the
utility. As well, new disposal regulations in the province of Nova Scotia will prevent the
disposal of alum residuals at municipal landfill sites beyond 2005. Although the
diversion from landfills is a specific policy to Nova Scotia, it is an approach that
addresses long-term sustainability.
Ferric coagulation plants are generally located in the United States, while alum
coagulation plants are located in both Canada and the United States. Residual availability
spans the continent, and residuals are abundant at most plants. Due to limited disposal
options, reuse is seen as a beneficial option. Previous research has shown that wet
solids 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 provided
only a mild benefit for phosphorus removal and the associated transportation/pumping
costs can be prohibitive for some utilities. Research has also shown that air dried residual
solids are capable of adsorbing phosphorus from P-spiked deionized water under a
variety of pH levels. The goal of this research is to examine oven dried residual
solids as an adsorbent for phosphorus removal, where oven drying has the added benefit
of increasing the surface area to volume ratio of available adsorbent and significantly
reduce 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 via
overnight 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 1
uses ferric sulphate as a coagulant, whereas the other three utilities use alum-based
coagulants. Among the alum-based plants, Plant 2 lime softens and has high
concentration of CaCO<sub>3</sub> in their dried solids. In contrast, Plant 3 has a raw water
alkalinity of 150-200 mg/L whereas Plant 4 has an alkalinity of less than 5 mg/L. Thus
this research will be able to compare the impact of alkalinity and coagulant type, using
the results of the batch adsorption experiments and an analysis of the residual solid
chemistry.
Batch adsorption experiments were conducted in three phases:
batch adsorption experiments with P-spiked deionized water to determine optimal
pH level and particle sizes using alum-based residuals;
batch adsorption experiments with buffered deionized water using the ideal
conditions determined in Phase 1; and,
batch adsorption experiments with municipal wastewater effluent and the ideal
conditions determined in Phase 1. Includes 9 references.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 130 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 5 |
| Published : | 11/01/2005 |
