Applications of vitrified powder and granular shales in the removal of inorganic phosphorus from industrial and municipal wastewaters.

摘要

Removal of phosphorus is a global environmental issue because excessive phosphorus (P) causes eutrophication, which impairs the quality of the surface and ground water resources. Industrial and municipal wastewaters contain significant quantities of P that should be removed to acceptable levels in order to alleviate the effects of eutrophication. Efforts aimed at reducing P in wastewater since the 70s have led to the current situation where wastewater treatment facilities discharge high volumes of treated effluents containing low concentration P (dominated by inorganic P) into surface water bodies. However, removal of P is expensive and is particularly difficult in the case of low P concentrations. In light of tightening P discharge standards, development of innovative, and cost effective P removal processes are required.;Lightweight expanded shale aggregates (LESA), a cheap ceramic based-mineral adsorbent and its derived by-product, shale-based flue dust (SFD), were investigated for use in removing inorganic P from treated wastewater effluents in a series of bench-scale tests, and a micro-pilot study using column beds. The adsorption of P onto these essentially macroporous adsorbents were fitted using Langmuir model. The process followed first-order kinetics, and was pH dependent. Maximum adsorption capacity varied inversely as the cube of mean aggregate size (D 50). Fractions of organic matter (OM) contained in treated effluent showed significant (p-value 0.05) competition for the adsorption sites on LESA and SFD surfaces, suggesting that OM fragments could be coating adsorption sites on the adsorbents surfaces.;Results of this study show that in the high strength P range, various doses of SFD consistently reduced inorganic phosphorus from 24.5 mg/L to 16.82-3.49 mg/L within one hour of mixing. In a low concentration P system, results show that LESA could be used in a column bed system to reduce P from 1.0 mg/L to 0.05 mg/L for 3 weeks. Overall, this research answered questions on the effects of process variables on use of LESA in the removal of inorganic P. It also answered questions relating to the potential of using LESA to remove low level P in a column bed. Design constants for use in such a system were also developed.