ABSTRACT
Sewage solids are usually characterized by non-specific parameters such as suspended solids. The suspended solids has been shown to be an inadequate index for advanced water treatment processes. In this study, the sewages solids particle size distribution was used to provide more detailed information on sewage characteristic. It is hoped that, by introducing particle size distribution, the mechanism of sewage solids sedimentations can be better understood. The particle size distribution of the domestic sewage was measured by the Malvern laser scattering technique to link to its settlement efficiency. Experimental results show that 77% of particle volume was removed during the 90 min settling, of which 71.2% of particle volume was removed in the initial 30 min. The submicron particles were found to be removed by co-settling with large particles. The fractal dimensions of sewage solids could also be derived from the laser scattering measurement. The fractal dimension could also provide useful information on the shape and density of sewage solids. A mathematical model considering the particle sizes, shapes and density changes was then constructed to simulate the settlement of raw sewage particles. Comparison of the modeling results based on discrete and flocculant settling theory shows that settlement can be better predicted by considering the fractal nature of particles. The particle size distribution and fractal dimension data measured by Malvern laser scattering technique have been shown to be valuable data for in-depth understanding of the mechanisms of sewage solids sedimentation
Subject(s)
Particle Size , Fractals , LasersABSTRACT
A suspended growth photobioreactor was utilized to treat pharmaceutical wastewater by a wild strain purple non-sulfur photosynthetic bacterium isolated from the soil. The strain was named Z08 and identified as Rhodobacter-sphaeroides by 16SrDN. The photobioreactor was illuminated externally with two [40 W] fluorescent compact light sources on both sides. Its operation pH and temperature were between 6.8 - 7.0 and 20 - 30°C, respectively. Optimum growth of the isolate was obtained after enrichment of the pharmaceutical wastewater with 0.5% ammonium sulfate and 0.1% yeast extract under microaerobic optimum light [6000 1x] condition at 5d retention. Using these optimum conditions, the maximum dry cell weight and chemical oxygen demand percentage removal were 880 mg/L and 80%. Chemical analysis of the culture after treatment of the enriched and non-enriched wastewater showed the crude protein content of the biomass to be 54.6% and 38.0%, respectively. This study proved that photosynthetic bacteria could transform complex wastewater that contains recalcitrant organic compounds with a resultant recovery of useful products