EFFECTS OF LIME‐SLUDGE DISCHARGE ON AN ARCTIC RIVER1

Abstract

ABSTRACT: The Fairbanks Water Treatment Plant in Fairbanks, Alaska, processes approximately 3 MGD of drinking water using lime softening. Approximately 0.3 MGD of lime‐sludge from the treatment process is combined with effluent from a nearby power plant and discharged to the Chena River. There is little information available on the impact of water‐treatment sludge discharges, and virtually no information on the impacts of such discharges in polar environments. Concern surrounding the discharge of water treatment sludges have centered on alum‐sludge due to the potential toxic effects of aluminum. Because of the relatively benign composition of lime‐sludge, very little research has been published. However, there is the possibility that discharge of solids will result in sedimentation, accumulation of solids, and subsequent impacts on benthic organisms. This paper reports on the results of a study to determine if lime‐sludge discharge from the water treatment plant is adversely impacting the river environment. The results provide basic information on the important variables of concern in lime‐discharges to rivers.Samples from the discharge of the water treatment plant and combined water treatment plant/power plant effluent were collected weekly over a one‐year period, and in‐stream benthic and water column samples were collected biweekly during the fall and spring. Sediment and water quality data indicate that while significant accumulation of sludge solids is found downstream of the water treatment plant outfall, they are flushed out of the system by spring flows, which are significantly increased by snow melt. This process is most likely repeated on a yearly cycle.Hence, the data suggest that the FMUS water treatment plant's discharge of lime‐sludge is probably not adversely impacting the river. More generally, this may indicate that the natural flow variations and sediment‐laden characteristics of Arctic, glacier‐fed rivers may assimilate large quantities of nonputrescible solids without significant changes in the natural river environment. Further research in this area is required to verify this conclusion.