H. K. Chui

Degradation of phenol in wastewater in an upflow anaerobic sludge blanket reactor

Abstract Phenol in wastewater could be effectively degraded in an upflow anaerobic sludge blanket (UASB) reactor. With a 1:1 effluent recycle ratio, over 97% of phenol was removed at 37°C and pH 6.9-7.5 with 12 h of hydraulic retention time for phenol concentration up to 1260 mg·1 −1 , corresponding to 3000 mg·1 −1 of chemical oxygen demand (COD) and a loading rate of 6 g-COD·1 −1 ·day −1 . The seed sludge took about 7 wk to develop the phenol-degrading capability which was sensitive to shocks. The bioactivity deteriorated readily when the granules were exposed to sudden changes of temperature and loading. Although the damage was not permanent, the recovery of bioactivity was gradual and lengthy. At 6 g-COD·1 −1 ·day −1 , each gram of granules was able to convert 0.49 g of COD into methane daily. On the average, about 94.7% of the total COD removed was converted to methane, while the rest was converted to biomass with a net yield of 0.038 g-VSS·(g-COD-removed) −1 . Electron micrographs show that the granules were composed of, among others, Syntrophus buswellii-, Methanothrix-, Methanospirillum- and Methanobrevibacter -like bacteria.

Microstructural analysis of UASB granules treating brewery wastewater

The microstructure of granules from a full-scale UASB reactor treating brewery wastewater was examined using light microscopy as well as the scanning and transmission electron microscopies. The granules typically have a complex, layered structure. The outer layer of the granule was densely packed with various types of bacteria, including cocci, bacilli, Methanosarcina , and Methanothrix . The second layer was composed of a matrix of Methanothrix with two types of microcolony showing evidence of syntrophic associations between hydrogen-producing acetogens and hydrogen-consuming methanogens. The interior of the granule, on the other hand, was predominantly Methanothrix with scattered microcolonies of syntrophic associations, which became sparse and disappeared toward the centre core of the granule.

Performance and sludge characteristics of UASB process treating propionate-rich wastewater

UASB process consistently removed 97–99% of chemical oxygen demand (COD) in wastewater containing concentrated propionate at 37°C in 12 h for loading rates up to 23 g-COD/1·day. Of all the COD removed, 95% was converted to methane and the rest was converted to biomass with an average sludge yield of 0.040 g-VSS/g-COD. Each gram of propionate-degrading granules in the reactor had a daily maximum capacity of converting 0.60 g of COD into methane. The granules were densely packed but did not exhibit any patterned microstructure. A typical propionate-degrading granule was composed of microcolonies of Methanothrix and several syntrophic microcolonies with hydrogen-producing acetogens in juxtaposition with hydrogen-consuming M. hungatei and Methanobrevibacter-like bacteria.

ANAEROBIC DEGRADATION OF BUTYRATE IN A UASB REACTOR

Abstract Wastewater with concentrated butyrate was treated in a 2·8 l UASB (Upflow Anaerobic Sludge Blanket) reactor at 37°C and pH 7·1–7·7. The process consistently removed 97–99% of COD for loading rates up to 31 g COD/l/day. Of all the COD removed, 94·5% was converted to methane; the average sludge yield was 0·037 g VSS/g COD. Conversion of acetate to methane appeared to be the rate-limiting step. Sludge granules had a maximum specific methane production rate of 1·57 g methane COD/g VSS/day, but were unable to degrade propionate. The granules were 1–2 mm in size and had a densely-packed skin layer which comprised two types of microcolony: one was composed of cocci with abundant extracellular polymer and the other was composed of two bacterial species in juxtapositioned syntrophic association. The interior was mainly composed of Methanothrix -like bacteria, a large number of which were entwined into rope-shaped aggregates.

Microstructural analysis of anaerobic granules

Photos of scanning and transmission electron microscopy showed that sludge granules treating sucrose wastewater had a 20–40 μm surface layer with diverse morphology, consisting of cocci and bacilli, and a loosely packed interior, mainly consisting of Methanothrix. Light microscopy using epi-fluorescent excitation showed not only the similar microstructure, but also the distribution of various genuses of methanogens.

Comparison of startup performance of four anaerobic reactors for the treatment of high-strength wastewater

Abstract An experimental study was carried out to compare the startup performance of four equal-volume anaerobic reactors of different design operated in parallel at 37°C. The four reactors, namely, (a) upflow anaerobic sludge blanket (UASB), (b) hybrid of UASB and anaerobic filter, (c) fluidized bed and (d) expanded bed, were seeded with sludge from the anaerobic digester of a local municipal wastewater treatment plant and tested with synthetic wastewater comprising milk and sucrose with balanced nutrients and trace metals. The volumetric COD loading was increased gradually from the initial 0.5–1 g L −1 d −1 to 20 g L −1 d −1 after 70 days. During this startup period, the COD levels in wastewater were gradually increased from the initial 500–1000 mg L −1 to 6500 mg L −1 , whereas the hydraulic retention time (HRT) was reduced from 24–48 h to 8 h. After the acclimation, the four reactors were tested at the loading rate of about 20 g L −1 d −1 , but at three different levels of COD (6000, 4000, 2600 mg L −1 ) and HRT (8, 5.7, 3 h). The percentage of COD removal from wastewater in an anaerobic reactor appeared to be mainly dependent on the volumetric COD loading rate, and relatively insensitive to the COD level in wastewater and the HRT. At the COD loading rate of about 20 g L −1 d −1 , COD reduction was about 95% for the UASB and the hybrid reactors, but was about 80% for the fluidized bed and expanded bed reactors.