Zoogleal clusters and sludge dewatering potential in an industrial activated-sludge wastewater treatment plant

Microscopic observations at an industrial wastewater treatment facility wer e conducted over a period of approximately 4 years to determine the relatio nship between the abundance of zoogleal clusters and sludge dewatering pote ntial. Dewatering potential, measured as centrifuged solids content, was de termined in sludge samples from an aeration basin. The abundance of zooglea l clusters and centrifuged solids content were negatively correlated, as de termined by linear regression (r(2) = 0.62). Curve-fitting using an exponen tially weighted moving average and a polynomial equation yielded r(2) = 0.8 2. Probing with small ribosomal subunit RNA (16S rRNA) oligonucleotide prob es (ZRA and ZEE) indicated that the microorganisms forming these zoogleal c lusters were not the same as previously classified Zoogloea ramigera strain s (members of the beta subclass of Proteobacteria) isolated from other wast ewater treatment systems. The microorganisms responsible for zoogleal clust er formation were identified using micromanipulator separation, cultivation , and 16S rRNA analysis. Distance matrix tree analysis of isolated strains revealed the presence of two types of microorganisms, referred to as mzt an d mzl strains. The mzt isolates grouped most closely with members of the ge nus Thauera, whereas the mzl isolates grouped more closely with members of the genus Hydrogenophaga. Using 16S rRNA methods, a probe complementary to members of the genus Thauera (MZ1; S-G-Thau-0646-a-A-19) was designed to ta rget mzt strains. Whole-cell hybridization with a fluorescein-labeled probe , coupled with epifluorescence microscopy, was used to verify the identity of the zoogleal cluster-forming organisms. Results indicated that the MZ1 p robe hybridized specifically with zoogleal clusters present in sludge.