Wastewater injection: near-well processes and their relationship to clogging
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1983
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University of Hawaii at Manoa
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Abstract
Well injection of treated wastewater almost inevitably results in aquifer clogging and reduced injection capacity. In Hawai'i clogging has produced well overflows resulting in numerous public health, legal, and financial problems. This study examines near-well processes, their relationship to clogging, and technology appropriate under Hawaiian hydrogeologic conditions for dealing with clogging. The first phase, monitoring of functioning injection sites, indicated that wells with poor quality injectant (average BOD5 and suspended solids each greater than 30 mg/l) generally have a high frequency of overflow. Although inconclusive with respect to clogging mechanism, results demonstrated the need for detailed studies at an experimental injection well system. The second phase, performed at the experimental well sites for the appropriate technology determination, had among its conclusions: need for selecting high initial injection capacity sites; need for periodic well redevelopment, the most effective means being compressed air and acid treatment followed by pumping; and need for standardization of pump and injection tests and for reduction factors (functions of initial injection capacity) to be applied to predict the maintainable capacity. The third phase included examination of injection stratum sediment and pore water sampled within one meter of the well. Results show that filtration of suspended solids is not a long-term cause of clogging as generally cited in the literature. It is probably a short-term cause at the start-up of effluent injection. Once the microbial biomass becomes established, it biodegrades the organic injected particulates. During the same period the denitrifying bacteria become sufficiently established to produce significant amounts of nitrogen gas. The N2 gas produces a gas-bound zone farther out in the aquifer as revealed by a shift in the head gradient. Initially most of the head loss is immediately adjacent to the well; after several weeks it shifts to a region over one-half meter from the injection well. This nitrogen gas-bound zone extends itself slowly farther out into the injection stratum. Superimposed on this. but its effects masked in part by the gas binding. is dissolution of the carbonate porous medium. which results in a flattening of the hydraulic gradient in non gas-bound regions.
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Wells, Aquifers, Refuse and refuse disposal
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Hawaii--Oahu
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Geology and Geophysics; no. 1662
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