Sulfate reduction for remediation of gypsiferous soils and solid wastes; Dissertation, UNESCO-IHE Institute for Water Education, Delft, Joint PhD degree in Environmental Technology.

Construction and demolition debris (CDD) and gypsiferous soils contain elevated concentrations of sulfate which can cause several environmental and agricultural problems. Reduction of the sulfate content of CDD and gypsiferous soils is an option to overcome these problems. This study aimed to develop sulfate removal systems either by biological or chemical processes to reduce the sulfate content of CDD and gypsiferous soils in order to decrease the amount of solid wastes and to improve the quality of CDD and soils for recycling purposes or agricultural applications. The treatment concept leaches the gypsum contained in the CDD by water. The sulfate containing leachate is further treated and reused in the leaching step. A mixture of cheap organic materials can be utilized as electron donor for the biological sulfate reduction step, especially in gypsiferous soils treatment. The sulfide containing effluent from the bioreactor can be removed by electrochemical sulfide oxidation system

Spontaneous electrochemical treatment for sulfur recovery by a sulfide oxidation/vanadium(V) reduction galvanic cell

Sulfide is the product of the biological sulfate reduction process which gives toxicity and odor problems. Wastewaters or bioreactor effluents containing sulfide can cause severe environmental impacts. Electrochemical treatment can be an alternative approach for sulfide removal and sulfur recovery from such sulfide rich solutions. This study aims to develop a spontaneous electrochemical sulfide oxidation/vanadium(V) reduction cell with a graphite electrode system to recover sulfide as elemental sulfur. The effects of the internal and external resistance on the sulfide removal efficiency and electrical current produced were investigated at different pH. A high surface area of the graphite electrode is required in order to have as less internal resistance as possible. In this study, graphite powder was added (contact area >633 cm(2)) in order to reduce the internal resistance. A sulfide removal efficiency up to 91% and electrical charge of more than 400 C were achieved when using five graphite rods supplemented with graphite powder as the electrode at an external resistance of 30 Omega and a sulfide concentration of 250 mg L-1

Chemical sulphate removal for treatment of construction and demolition debris leachate

Construction and demolition debris (CDD) is a product of construction, renovation or demolition activities. It has a high gypsum content (52.4% of total gypsum), concentrated in the CDD sand (CDDS) fraction. To comply with the posed limit of the maximum amount of sulphate present in building sand, excess sulphate needs to be removed. In order to enable reuse of CDDS, a novel treatment process is developed based on washing of the CDDS to remove most of the gypsum, and subsequent sulphate removal from the sulphate-rich CDDS leachate. This study aims to assess chemical techniques, i.e. precipitation and adsorption, for sulphate removal from the CDDS leachate. Good sulphate removal efficiencies (up to 99.9%) from the CDDS leachate can be achieved by precipitation with barium chloride (BaCl2) and lead(II) nitrate (Pb(NO3)2). Precipitation with calcium chloride (CaCl 2), calcium carbonate (CaCO3) and calcium oxide (CaO) gave less efficient sulphate removal. Adsorption of sulphate to aluminium oxide (Al2O3) yielded a 50% sulphate removal efficiency, whereas iron oxide-coated sand as adsorbent gave only poor (10%) sulphate removal efficiencies

Use of organic substrates as electron donors for biological sulfate reduction in gypsiferous mine soils from Nakhon Si Thammarat (Thailand)

Soils in some mining areas contain a high gypsum content, which can give adverse effects to the environment and may cause many cultivation problems, such as a low water retention capacity and low fertility. The quality of such mine soils can be improved by reducing the soil's gypsum content. This study aims to develop an appropriate in situ bioremediation technology for abbreviating the gypsum content of mine soils by using sulfate reducing bacteria (SRB). The technology was applied to a mine soil from a gypsum mine in the southern part of Thailand which contains a high sulfate content (150gkg-1). Cheap organic substrates with low or no cost, such as rice husk, pig farm wastewater treatment sludge and coconut husk chips were mixed (60:20:20 by volume) and supplied to the soil as electron donors for the SRB. The highest sulfate removal efficiency of 59% was achieved in the soil mixed with 40% organic mixture, corresponding to a reduction of the soil gypsum content from 25% to 7.5%. For economic gains, this treated soil can be further used for agriculture and the produced sulfide can be recovered as the fertilizer elemental sulfur

Sulfate Ion Removal from Reverse Osmosis Concentrate Using Electrodialysis and Nano-Filtration in Combination with Ettringite Precipitation

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