Sedimentation of Raw Sewage: Investigations For a Pumping Station in Northern Germany under Energy-Efficient Pump Control

Abstract

Flow control in wastewater pressure pipes can reduce energy consumption but increases the risk of sediment formation due to reduced flow velocity. In this work, the sedimentation behavior of dry and wet weather samples at the inflow of a wastewater pumping station is determined by settling column experiments. Based on the derived characteristic settling velocity (vs) distribution, the impact of energy-efficient flow control on sediment formation in pressure pipes (600 mm diameter) was quantified in comparison to a simple on/off operation. In parallel, the sediment formation for 2 years of pumping operation was monitored indirectly via the friction losses. For the investigated case, settling is strongly influenced by the inflow condition (dry, combined from road runoff). Under combined inflow, the proportion of solids with vs from 0.007 to 1.43 mm/s significantly increases. In energy-efficient mode with smoother operation and shorter switch-off sequences, the sediment formation is significant lower. The mean deposit’s height in energy-efficient control was calculated to 0.137 m, while in on/off operation the mean deposit’s height was 0.174 m. No disadvantages arise over a long period by installing the energy-efficient control. The decreased flow lead under the investigated conditions even to a reduced sediment formation.

Sediment Transport in Sewage Pressure Pipes, Part II: 1 D Numerical Simulation

“…A parallel storm sewer receives the residual surface and roof runoff. Additional information about the study area are provided by [1][2][3] which includes a detailed schematic view of the sewer system and PS Rostock-Schmarl.…”

“…These rules are defined by the operator to ensure solids transport and to avoid blockages. For detailed information about the control modes, read [1,22,23].…”

“…The sediment layer at pipes invert is then a superposition of different solid fractions. The settling behavior of various particle fractions can be described as a settling velocity distribution, as conducted in [1]. The computation of several particle fractions is useful for dealing with pollutant transport when specific fractions contain more pollutants than other components (see [24]).…”

“…Hence, the following simplifications are assumed for the simulation. The sedimentation of different solid fractions, as described in [1], is not considered. The settling process is described as an exponential decay of solids, similar to [3].…”

“…Especially with regard to sedimentation and erosion, a numerical simulation is now of interest. Within a case study in an urban region in northern Germany (city of Rostock), solids transport inside a pressure pipe was investigated within several ex situ (laboratory) experiments [1,2] and continuously monitored by in situ turbidity measurements for one year under energy efficient pump control [3]. However, the energy efficient control was only permitted in certain range of operation conditions.…”