H2S Removal from Industrial Wastewater Using Biofilm Airlift Suspension reactor

1. One of the main reasons for dissatisfaction of industrial wastewater neighbors is odor emissions caused by compounds such as hydrogen sulfide [1]. Physical and chemical methods are used for removing hydrogen sulfide. These systems are expensive because of their high energy demand and operating costs. Biological treatment processes are often used to overcome these problems [2]. Thiobacillus thioparus was used for hydrogen sulfide treatment of industrial wastewater [3]. Different types of bioreactors have been used for H2S removal by chemotrophic bacteria. These include gas-fed batch reactors, fixed-film upflow reactor, biorotor, continuous-flow reactors, bioscrubbers, biofilter, and biotrickling filter. Biofilm Airlift Suspension (BAS) reactor is a novel biological wastewater treatment process that has been evaluated extensively [4]. The aim of this work is to develop a biofilm airlift suspended reactor using basalt as solid support for T. thioparus (PTCC 1668) for the first time to remove H2S from synthesized and industrial wastewater.2. 2.1. Reactor and operating conditionsA laboratory scale airlift reactor with a volume of 4.2 L made of Shott glass was used in this study. Fig. 1 shows a schematic representation of the experimental setup. The temperature was maintained at 30±1 oC using a thermostated water jacket. The pH of the influent was 7. T. thioparus TK-1 was got from a Persian type culture collection (PTCC, 1668). Hydrogen sulfide was analyzed using silver/sulfide ion electrodes (Cole Parmer, Cat. No. 27502–41), and sulfate by a turbidimetric method with a spectrophotometer. Mixed liquor volatile suspended solids were determined according to the Standard Method 2540E. Biofilm development was determined by removing a sample from the reactor. The mean biofilm diameter and standard deviation were calculated from about 50 randomly selected particles observed with an Olympus PMG 3-AN microscope.3. 3.1. Results of operating reactor with synthesized wastewaterMicroscopic observations showed that, because feed was not sterile, protozoa was existent in the low sulfide loading rate (2.4 mol S2- m-3 h-1). But with rising sulfide loading rate to 4.8 mol S2- m-3 h-1, the protozoa was not behold in the reactor. Maximum sulfide oxidation rate was12.2 mol S2- m-3 h-1 occurring in residence time of 1.3 h.3.2. Results of operating reactor with industrial wastewaterDuring the experiments with industrial wastewater, sulfide loading rate was raised from 36 mg.L-1.h-1 to 683 mg.L-1.h-1, though the sulfide concentration in the reactor outlet was zero. In the BAS reactor, inside the reactor due to the high oxygen is a significant amount of sulfide converted to sulfate. However, in the high concentrations of sulfide due to inhibition of sulfide sulfur not converted to sulfate. This will reduce the ratio of sulfate to sulfide or in other words, ratio of sulfides converted to sulfur.3.3. characteristic of biofilm:Results of microscopic observations on Basalt carrier and biofilm formation showed in Fig. 2. Starting of biofilm formation was occurred on dip of basalt. With continuing, the biofilm com to flat in dip was full and biofilm diameter in dip was more than the other.4. In this study, the performance of BAS-reactor for H2S oxidation from synthesized wastewater in different loading rate was examined. The maximum sulfide oxidation rate reached in synthesized wastewater was about 12.2 mol S2-m-3h-1 at a hydraulic residence time of 3.3 h. During the experiment, most of the sulfide oxidized to sulfate.