Treatment of surface water rich in humus — Membrane filtration vs. conventional treatment

Abstract

The investigated raw water from lake Muskan, Nynäshamn community, has a high color content of mainly humic substances (up to 100 mg Pt/l) and also taste and odor problems, particularly during the algae blooming period. Membrane filtration of this raw water is one of the alternatives suggested for the future drinking water production (6,000 m 3/d) in Nynäshamn community. This paper includes mainly the results of laboratory trials in order to evaluate tested membranes (ceramic MF and UF membranes, polymeric UF and NF membranes) with respect to the need of activated carbon treatment as well as for comparison with corresponding results of laboratory trials with conventional flocculation/sedimentation/filtration and activated carbon treatment. The intention has been to select the most feasible membrane method for trial operation in a pilot plant. The latter stage of this project will be reported in a separate paper.IInitial testing was performed, with and without activated carbon treatment, of nine UF and NF membranes with nominal cut-off values varying between about 180 and 20,000 as well as of four ceramic MF and UF membranes. Further concentration trials in combination with membrane cleaning were done with four selected membranes-two NF membranes and two UF membranes (cut-off 20,000 and about 2,000). The purification parameters used for evaluation were primarily color, TOC (DOC) and COD-Mn. The efficiency of added powdered activated carbon (6 mg/l) in the influent before the membrane filtration was negligible. The removal of color and organic matter was almost complete (undetectable levels) with nanofiltration. Activated carbon treatment of the permeate was required with the UF membranes. However, the adsorption isotherm with the selected quality of activated carbon showed low adsorption capacities. As a conclusion of the overall laboratory trials it was stated that nanofiltration of the raw water from lake Muskan is an interesting alternative for the future drinking water production within Nynäshamn community. It was thus recommended to perform trial operation in a pilot plant for design of a full-scale plant. The costs are at present a little higher with the membrane method compared to conventional treatment including activated carbon, but the drinking water quality is better and more consistent.