Solar photocatalytic oxidation of pretreated wastewaters: laboratory scale generation of design data for technical-scale double-skin sheet reactors.

Batchwise heterogeneous photocatalytic oxidation of model wastewater (solutions of the azo dye "Acid Orange 7" in tap water) has been performed in a laboratory-scale stirred vessel reactor with non-submerged UV-A lamps using titanium dioxide "P25" as photocatalyst. Comparison to results of solar pilot-scale Plexiglass double-skin sheet reactor (DSSR) experiments indicates that the lab-scale method may predict area demand for technical-scale DSSR design. Characteristic UV-A fluences leading to TOC or COD reduction to e(-1) of the initial concentrations were determined in lab-scale stirred vessel experiments for treated effluents of seven different industrial branches, secondary municipal effluent and biologically treated greywater. Predicted areas for solar photocatalytic oxidation of these effluents in DSSRs yielding mineralization of 95% of organics in 100 m3 of the respective effluents for a TiO2 concentration of 2 g l(-1) and a sky and solar radiation of 3.9kWh m(-2) d(-1) within one day greatly varied from below 6,000 m2 (biologically treated lubricating oil refinery effluent) to more than 100,000 m2 (highly saline biologically treated effluent of chemical industry). Especially municipal and refinery effluents (except oil reclaiming) have been identified as promising candidates for reuse after solar photocatalytic oxidation. Mineralization efficiency was decreasing with increasing alkalinity of effluents. This was interpreted by competition of hydrogen carbonate anions with organics for binding sites on photocatalyst surface and by OH radical scavenging by hydrogen carbonate. Dependence on alkalinity was superimposed by salinity influence as some effluents with high alkalinity also exhibited high salt concentrations (especially chloride).

Freeze concentration for enrichment of nutrients in yellow water from no-mix toilets.

Separately collected urine ("yellow water") can be utilized as fertilizer. In order to decrease storage volumes and energy consumption for yellow water transport to fields, enrichment of nutrients in yellow water has to be considered. Laboratory-scale batch freeze concentration of yellow water has been tested in ice-front freezing apparatus: a stirred vessel and a falling film freeze concentrator (coolant temperatures: -6 to -16 degrees C). With progressing enrichment of the liquid concentrate, the frozen ice was increasingly contaminated with yellow water constituents (ammonia, total nitrogen, total phosphorus, TOC, and salts determined as conductivity). The higher the initial salinity of the yellow water and the lower the mechanical agitation of the liquid phase contacting the growing ice front, the more the frozen ice was contaminated. The results indicate, that in ice-front freezing devices multistage processes are necessary, i.e. the melted ice phase has to be purified (and the concentrates must be further enriched) in a second or even in a third stage. Energy consumption of this process is very high. However, technical scale suspension freeze concentration is reasonable in centralized ecological sanitation schemes if the population exceeds 0.5 million and distance of yellow water transportation to fields is more than 80 km.

Fungi in activated sludge biocenosis.

It has been found that yeasts and yeast-like microorganisms are stable constituents of activated sludge biocenosis treating municipal wastewaters with a mixture of different industrial wastewaters at B upsilon values in the range of 1.3-1.7 kg COD m-3day-1 and B chi = 0.22-0.42 kg COD kg-1day-1. The number of these microorganisms reached about 10(4) cells mg VSS-1 and as typical species Saccharomyces cerevisiae and Candida famata can be considered. Considerably less numerous (4-8 cells mg VSS-1) was the mycoflora of high loaded treatment systems of petrochemical wastewaters (B upsilon = 10.3-14.1 kg COD m-3day-1 and B chi = 1.06-1.92 kg COD kg-1day-1) and municipal wastewaters with a mixture of aromatic amines (B upsilon = 1200-2400 mg COD l-1 day-1 and B chi = 0.43-0.94 mg COD mg-1day-1). Typical species for these sludges were Geotrichum candidum, G.klebahnii, G.sericeum, Trichosporon cutaneum and Sporobolomyces lactosus.