Some Simple Approaches for Turbidity Reduction in Pumped Water

摘要

Many construction projects involve the need to pump turbid water from borrow pits or other excavations into stilling basins or sediment bags prior to discharge. The design and operation of these treatments needs to be optimized to provide the best water treatment prior to discharge. This project was designed to provide an evaluation of stilling basin designs and polyacrylamide (PAM) injection to minimize turbidity in discharged water. Of particular interest were difficult to settle Coastal Plain sediments containing highly charged clays (smectite/montmorillonite). The use of stilling basins did not result in significant reductions in turbidity in water pumped from the simulated borrow pits in these types of soils. Anionic PAM did not sufficiently reduce turbidity for these sediments but they were flocculated by neutral or cationic PAM. In field tests, introducing PAM solutions into the pump intake at a rate of 5 mg L~(-1) reduced turbidity by up to 98%. Porous baffles made of rock or coir and jute did not improve on the PAM treatment effect. However, at least one baffle is recommended when PAM is being used in case floating floes are formed. Turbidity was reduced from the 500-800 NTU range to < 30 NTU in many cases, especially for the cationic PAM. Similar reductions were achieved using a sediment bag. Toxicity tests indicate the relative PAM toxicity was cationic > anionic > neutral, and was not affected by turbidity. The neutral PAM was almost as effective as the cationic PAM and was even less toxic than the anionic PAM, so it may be an alternative where the anionic PAMs that are available will not work.