Biotechnological sulphide removal with oxygen

English. This thesis deals with the development of a new process for biotechnological sulphide removal from wastewater, in which it is attempted to convert sulphide into elemental sulphur by colourless sulphur bacteria. The toxicity, corrosive properties, unpleasant odor and high oxygen demand of sulphide dictate stringent control of its release into the environment. The goals of the research were: development an efficient and reliable high rate treatment system for purification of sulphide containing wastewaters and assessment of the conditions that promote sulphur instead of sulphate formation.The newly developed biotechnological sulphide removal system accomplishes a removal rate and efficiency which at least is similar to that of other sulphide removal systems, which are based on the oxidation with air. Application of the system is possible in the pH range 6.5 - 9.0 and in a temperature range of approximately 15 - 40 °C.At least two types of sulphide oxidizing bacteria were found, viz. a sulphate producing (type A) and a sulphur producing bacteria (type B). Type A is inhibited by sulphide and type B by oxygen. As the conversion of sulphide into sulphur is the main aim of the system, growth of type B should be stimulated. This can be accomplished by imposing high sulphide loading rates (>200 mg/l.h) and maintaining low oxygen concentrations (< 4 mg/l). The growth yield of type B (0.3 g DS/mol S) is lower than that of type A (3 g DS/mol S), and therefore little biological sludge will be produced when sulphur is the end-product.The start-up of the system is fast, viz. 5 days in a CSTR (1% inoculum), when applying a sulphide influent concentration of 100 mg/l and a HRT of 22 minutes. The oxygen concentration should not exceed 4 mg/l, because inhibition of type B should be prevented.The noncatalyzed chemical sulphide oxidation (at oxygen concentration 4 mg/l) is considerably slower (75 times) than the biological sulphide oxidation at sulphide concentrations below 10 mg/l and about a factor 6 at sulphide concentrations up to 600 mg/l.In a sulphide reactor merely two groups of unwanted bacteria can develop, viz. bacteria that store the sulphur inside the cell and cause sludge bulking problems, like Thiothrix and bacteria that produce sulphide like Desulfuromonasacetoxidans (sulphur reducer) and Desulfobulbuspropionicus (sulphate reducer). Both groups of bacteria can only develop, when organic compounds are present in the wastewater. The problems caused by unwanted bacteria can be minimized by applying high sulphide loading rates (prevention of Thiothrix growth) and a high rotation speed (prevention of the sulphide producing bacteria). The sulphur reducing bacteria, present in the sludge, can use acetate but not propionate, while the sulphate reducing bacteria use propionate but not acetate.When the newly developed process is applied on anaerobically treated papermill wastewater using a biorotor reactor, a removal rate of 620 mg/l.h) at a removal efficiency of 95% is found at a HRT of 13 minutes, while only 8% of the sulphide is converted to sulphate.

Dutch; Flemish. Beschrijving van het onderzoek naar een nieuw biotechnologisch proces voor sulfideverwijdering, waarbij getracht wordt sulfide in zwavel om te zetten m.b.v. de kleurloze zwavelbacterien. De doelstellingen van het onderzoek waren de ontwikkeling van een efficient en betrouwbaar verwijderingssysteem voor de zuivering van sulfide-bevattende afvalwaters en de vaststelling van de condities, waaronder sulfide in zwavel wordt omgezet i.pl.v. in sulfaat