Estimation of the specific surface area for a porous carrier.

In biofilm systems, treatment performance is primarily dependent upon the available biofilm growth surface area in the reactor. Specific surface area is thus a parameter that allows for making comparisons between different carrier technologies used for wastewater treatment. In this study, we estimated the effective surface area for a spherical, porous polyvinyl alcohol (PVA) gel carrier (Kuraray) that has previously demonstrated effectiveness for retention of autotrophic and heterotrophic biomass. This was accomplished by applying the GPS-X modeling tool (Hydromantis) to a comparative analysis of two moving-bed biofilm reactor (MBBR) systems. One system consisted of a lab-scale reactor that was fed synthetic wastewater under autotrophic conditions where only the nitrification process was studied. The other was a pre-denitrification pilot-scale plant that was fed real, primary-settled wastewater. Calibration of an MBBR process model for both systems indicated an effective specific surface area for PVA gel of 2500 m2/m3, versus a specific surface area of 1000 m2/m3 when only the outer surface of the gel beads is considered. In addition, the maximum specific growth rates for autotrophs and heterotrophs were estimated to be 1.2/day and 6.0/day, respectively.

Treatment of high-strength corn steep liquor using cultivated polyvinyl alcohol gel beads in an anaerobic fluidized-bed reactor.

Polyvinyl alcohol (PVA) gel beads cultivated in an upflow anaerobic sludge-blanket reactor treating synthetic corn steep liquor (CSL) wastewater were used to seed a lab-scale anaerobic fluidized-bed (AFB) reactor also treating CSL. Under steady-state conditions in the AFB reactor, a COD removal efficiency in excess of 96% was achieved at an organic loading rate (OLR) of 25 g/l/d with a hydraulic retention time (HRT) of 10 h. Furthermore, a removal efficiency of 91% was achieved at an OLR of 27.5 g/l/d with an HRT of only 6 h. With a biomass attachment 1.02 g VSS/g PVA-gel beads, the biomass concentration in the AFB reactor was approximately 610 g/l, while for natural granules only 100 g/l is considered possible. Over the study period, the granular PVA gel turned from black to gray while the biomass attached on the outer surface of the beads also changed in composition. In addition, observations of the interior of the gel beads showed that colonization had progressed well into the core, indicating that effective substrate diffusion occurred within the PVA-gel matrix under the good substrate-microorganism contact conditions provided by the AFB reactor.

Maintaining granulation in a denitrifying upflow sludge-blanket reactor treating groundwater with low hardness.

Maintenance of denitrifying granular sludge for treating soft groundwater (total hardness = 75 mg calcium carbonate/L) in an upflow sludge-blanket reactor was demonstrated with complete removal of applied nitrate (20 mg N/L) over extended operation and a hydraulic residence time of 34 minutes. A high pH of approximately 9.0 was shown to be important for generation of mineral precipitation needed for production of heavy granular sludge with good retention characteristics. As a method of increasing precipitation potential, pH adjustment was determined to be more economically favorable than calcium or alkalinity supplementation. In addition, temporary increases in substrate loading were shown to be effective for enhancing biomass levels in a manageable granular sludge. The significance of biomass in promoting mineral precipitation was discussed.

Characterization of the microbial community in an anaerobic ammonium-oxidizing biofilm cultured on a nonwoven biomass carrier.

The enrichment and characterization of anaerobic ammonium-oxidizing biofilm cultures are ongoing in our laboratories. Biomass, with a predominately red color, demonstrating simultaneous removal of ammonium and nitrite under autotrophic and anoxic conditions, which is characteristic of anaerobic ammonium-oxidizing planctomycetes, was enriched and maintained for an extended period on a polyester nonwoven carrier. To investigate the bacterial composition of the mature biofilm community, 16S rDNA sequences were amplified by PCR and comparative analyses using DNA databases were conducted. Only one sequence had a notable similarity (92.2%) to that of the first discovered anaerobic ammonium-oxidizing planctomycete and lesser, yet significant, similarities to the 16S rDNA sequences of other recently reported anaerobic ammonium-oxidizing strains. The newly discovered strain (designated KSU-1) reported here was dominant among detectable members of the biofilm community. By fluorescence imaging, KSU-1 was shown to form spherical clusters wrapped in a thin layer of Zoogloea sp. Possible interactions and interdependencies of these two species are discussed with regard to the putative unculturability of the anaerobic ammonium-oxidizing planctomycetes.