Biofilter for generation of concentrated sulphuric acid from H2S.

Biofilters are used for the conversion of odorous hydrogen sulphide to odourless sulphate in wastewater treatment plants under the right conditions of moisture and pH. One of the consequences of maintaining the suitable pH and moisture content is the production of large volumes of weakly acidic leachate. This paper presents a biofilter with a maximum H2S elimination capacity of 16.3 g m(-3) h(-1) and removal efficiency greater than 95 % which produces small volumes (1 mL of solution L(-1) of reactor day(-1)) of sulphuric acid with a concentration greater than 5.5 M after 150 days of continuous operation. The concentrated sulphuric acid was produced by intermittently trickling a minimum amount of nutrient solution down the upflow biofilter which created a moisture and pH gradient within the biofilter resulting in an environment at the top for the bacterial conversion of H2S, while sulphuric acid was accumulated at the base. Genetic diversity profiling of samples taken from different sections of the biofilter confirms that the upper sections of the biofilter had the best environment for the bacteria to convert H2S to sulphate. The formation of concentrated sulphuric acid presents an opportunity for the recovery of sulphur from the waste stream as a usable product.

Enhancement of waste activated sludge anaerobic digestion by a novel chemical free acid/alkaline pretreatment using electrolysis.

Anaerobic digestion of waste activated sludge (WAS) is relatively poor due to hydrolysis limitations. Acid and alkaline pretreatments are effective in enhancing hydrolysis leading to higher methane yields. However, chemical costs often prohibit full-scale application. In this study, 12 V two-chamber electrolysis using an anion exchange membrane alters sludge pH without chemical dosing. pH dropped from 6.9 to 2.5 in the anode chamber and increased to 10.1 in the cathode chamber within 15 h. The volatile suspended solids solubilisation of WAS was 31.1% in the anode chamber and 34.0% in the cathode chamber. As a result, dissolved chemical oxygen demand increased from 164 to 1,787 mg/L and 1,256 mg/L in the anode and cathode chambers, respectively. Remixing of sludge from the two chambers brought the pH back to 6.5, hence no chemical neutralisation was required prior to anaerobic digestion. Methane yield during anaerobic digestion at 20 d retention time was 31% higher than that of untreated sludge. An energy balance assessment indicated that the non-optimised process could approximately recover the energy (electricity) expended in the electrolysis process. With suitable optimisation of treatment time and voltages, significant energy savings would be expected in addition to the benefit of decreased sludge volume.

Maternal lymphocyte subsets in the cases with neural tube defects.

Neural tube defects (NTDs) are among the most prevalent of congenital malformations. Organ system anomalies and certain changes in the thymus gland have also been reported. Lymphocyte subset changes can be expected in infants with NTD as a result of these thymic anomalies. We investigated lymphocyte subpopulations in twenty-one mothers of NTD cases in order to evaluate the maternal immunological alterations. The mothers of twenty-one healthy infants were chosen as a control group. Pregnancy is known to be associated with a depression in cellular immunity. We found, however, some additional changes in cellular immunity in the mothers of NTDs. The CD4/CD8 ratios were significantly lower than those of control mothers (p = 0.044). This difference was related to the increased percentage of CD8 cells found in mothers of NTDs (p = 0.004). These results suggest that immunosuppression is more evident in the mothers of babies with NTDs.