The Role of Membrane Filter Presses in Municipal Wastewater

Municipal sludge is different from industrial sludge. It has a very high moisture content and a large organic fraction, and the water in the sludge is tightly bound within the floc structure. Ordinary filter presses can usually only reduce the moisture content to around 80%, and it is difficult to go lower. Cake that is too wet has a large volume and high transportation and disposal costs, and many wastewater treatment plants therefore face pressure to meet discharge compliance requirements.

The membrane filter press solves this “final squeeze” problem. After feeding is completed, the membrane applies a second high-pressure squeeze to the filter cake, forcing out part of the water that ordinary filtration cannot remove. The effect is direct: the cake moisture content can be 10–15 percentage points lower than that of an ordinary filter press, and municipal sludge can be stably reduced to below 60%.

A municipal wastewater treatment plant in Weihai, Shandong, provides a practical operating case. The plant has a daily treatment capacity of 60,000 tons. Its original two belt filter presses had a sludge moisture content consistently above 80%, failing to meet the requirement that “sludge leaving the plant must have a moisture content below 60%.” The plant later selected a 250 m² fully automatic water-flushing membrane filter press (in practice, two units operating in parallel). After commissioning, the cake moisture content stabilized at 58%–63%, with the lowest batch reaching 55%.

Reducing the moisture content from 80% to below 60% brings very practical changes. Sludge volume is greatly reduced, and the outbound disposal volume is cut by about half. The number of transport trips, the feed volume for landfill or incineration, and the whole-chain disposal costs all decline accordingly. For a medium-sized wastewater treatment plant, the 250 m² specification can cover daily sludge output while retaining a certain margin. Automatic plate pulling and online water flushing also reduce manual operation and filter cloth clogging problems.

Simply put, the membrane filter press plays the role of the “final reduction checkpoint” before sludge leaves a municipal wastewater treatment plant. The drier the cake is pressed and the smaller its volume, the more options are available for subsequent transportation, disposal, and resource utilization, and the lower the pressure on the entire sludge treatment chain.