Hai-Lou Xu

Mechanisms and models for anaerobic granulation in upflow anaerobic sludge blanket reactor

Upflow anaerobic sludge blanket (UASB) reactor has been employed in industrial and municipal wastewater treatment for decades. However, the long start-up period required for the development of anaerobic granules seriously limits the application of this technology. In order to develop the strategy for rapid UASB start-up, the mechanisms for anaerobic granulation should be understood. This paper attempts to provide a up-to-date review on the existing mechanisms and models for anaerobic granulation in the UASB reactor, which include inert nuclei model, selection pressure model, multi-valence positive ion-bonding model, synthetic and natural polymer-bonding model, Capetowns model, spaghetti theory, syntrophic microcolony model, multi-layer model, secondary minimum adhesion model, local dehydration and hydrophobic interaction model, surface tension model, proton translocation-dehydration theory, cellular automaton model and cell-to-cell communication model. Based on those previous works, a general model for anaerobic granulation is also proposed. It is expected that this paper would be helpful for researchers to further develop a unified theory for anaerobic granulation and technology for expediting the formation of the UASB granules.

Anaerobic granulation technology for wastewater treatment

Anaerobic wastewater treatment using granular sludge reactors is a developing technology, in which granular sludge is the core component. So far, around 900 anaerobic granular sludge units have been operated worldwide. Although intensive research attention has been given to anaerobic granules in the past 20 years, the mechanisms responsible for anaerobic granulation and the strategy of how to expedite substantially the formation of granular sludge have not yet been completely clear. This paper reviews the mode of anaerobic granulation, including the mechanisms and models for anaerobic granulation, major factors influencing anaerobic granulation, characteristics of anaerobic granules, anaerobic granulation in other types of reactors, industrial application of anaerobic granulation technology and neural fuzzy model-based control strategy developed for anaerobic systems. Some approaches for future research are outlined.

Anaerobic granulation with methanol-cultured seed sludge.

A new biotechnology on sludge granulation in upflow anaerobic sludge blanket (UASB) system was developed in this study. Methanol-cultured sludge for UASB inoculation demonstrated a beneficial effect on the granulation process. This new biotechnology accelerated the formation of embryonic granules in a laboratory-scale UASB reactor, and the granulation process reached its post-maturation stage in about 15–20 days ahead of the control reactor. There were no significant negative effects on COD removal and gas production due to this methanogen-enriched seed sludge. Methanol-cultured seed sludge for UASB inoculation could be an effective method to reduce the time required for UASB system start-up.

Feasibility study on the operation of UASB reactor treating acidified food waste.

ABSTRACT A mesophilic upflow anaerobic sludge blanket (UASB) reactor seeded with granules adapted to VFA wastewater was operated as the methanogenic phase of a two-phase anaerobic batch process for food waste digestion. A semi-liquid recycle reactor filled with food waste was used as the acidification reactor and first recirculated for 8 days in the pre-acidification stage, resulting in 14,500 mg/L of total VFA and 15,800 mg/L of COD in the leachate. During the subsequent 8 days of two-phase operation, the leachate was circulated to the UASB reactor. In methanogenic phase, biogas with methane content of 68% on average was generated, and COD and total VFA removals were 74–93% and 77–99%, respectively. At the end of two-phase process, 65% of volatile solids removal and 0.30 L/gVS of methane yield were obtained. The results of this laboratory-scale study show that an UASB system can be used as the methanogenic phase in a two-phase anaerobic batch process, and is effective for conversion of the acidified food waste.

Preserved granular sludge for inoculation of new UASB reactors

In this study, granular sludges collected from a mesophilic laboratory-scale UASB reactor were stored for 6 months at 4°C, 24°C (room temperature) and 35°C, respectively. The preservation characteristics of granular sludges (including soluble COD, granular particle size and granular surface morphology) in terms of storage age and temperature were investigated. It was found that 4°C stored UASB granules were more capable of maintaining their granular structures over those stored at 24°C and 35°C. Granulation in UASB reactors seeded with preserved sludge granules reached its post-maturation stage about 40 days ahead of the control, mainly by means of eliminating the embryonic granule formation stage from the granulation process. The results in this study indicated that the preserved granular sludge could be used as an effective inoculum to accelerate new UASB reactor start-up.