• Energy Research

This study investigated the role of sludge retention time (SRT) in aerobic granulation under negligible hydraulic selection pressure. Results showed that no successful aerobic granulation was observed at the studied SRTs in the range of 3-40 days. A comparison analysis revealed that hydraulic selection pressure in terms of the minimum settling velocity would be much more effective than SRT for enhancing heterotrophic aerobic granulation in sequencing batch reactor (SBR). It was shown that SRT would not be a decisive factor for aerobic granulation in SBR.

Tetracycline has been frequently detected in municipal wastewater due to its extended use for various purposes. This study investigated the influence of tetracycline on non-aerated microalgal-bacterial granular sludge cultivated for municipal wastewater treatment. It was found that ammonia-N removal rate decreased at the tetracycline concentrations of 1 and 10 mg/L. A mass balance on nitrogen further revealed that the observed ammonia-N removal could be mainly attributed to microalgal assimilation which was inhibited by tetracycline at the concentrations studied. In fact, reduced production of chlorophyll in microalgae was observed in the presence of tetracycline, leading to decreased ammonia-N removal rate. Meanwhile, decreased dissolved oxygen (DO) concentration at high tetracycline concentration also indicated inhibition of microalgae. Furthermore, the relative abundances of microalgae containing green algae and cyanobacteria were inhibited by tetracycline. The results gathered in this study indicated the tetracycline-induced decoupling of symbiosis in microalgal-bacterial granular sludge. It is expected that this study can shed lights on the behaviors of non-aerated microalgal-bacterial granules in response to the presence of tetracycline during municipal wastewater treatment.

In this study, a fungal mash rich in hydrolytic enzymes was produced by solid state fermentation (SSF) of waste cake in a simple and efficient manner and was further applied for high-efficiency hydrolysis of mixed food wastes (FW). The enzymatic pretreatment of FW with this fungal mash resulted in 89.1 g/L glucose, 2.4 g/L free amino nitrogen, 165 g/L soluble chemical oxygen demand (SCOD) and 64% reduction in volatile solids within 24h. The biomethane yield and production rate from FW pretreated with the fungal mash were found to be respectively about 2.3 and 3.5-times higher than without pretreatment. After anaerobic digestion of pretreated FW, a volatile solids removal of 80.4±3.5% was achieved. The pretreatment of mixed FW with the fungal mash produced in this study is a promising option for enhancing anaerobic digestion of FW in terms of energy recovery and volume reduction.

According to the Food and Agricultural Organization (FAO), one-third of food produced globally for human consumption (nearly 1.3 billion tons) is lost along the food supply chain. Food waste has often been incinerated with other combustible municipal wastes for possible recovery of heat or other forms of energy, and the residual ash is disposed of in landfills. However, incineration is not cost-effective, and can potentially cause air pollution. Therefore, green technology is urgently needed for appropriate management of food waste with a focus on material recovery. Due to its organics- and nutrients-rich nature, food waste could be viewed as a useful resource for production of high-value platform chemicals through fermentation. Compared with animal feed or traditional fuel for transportation, platform chemicals obviously have higher economic value, i.e. more profitable. Recently, technologies for production of value added bio-products (e.g. organic acids, biodegradable polymers, etc.) from various kinds of food wastes have gained more and more interest. This review attempts to examine the state of the art of the fermentation technologies of food waste for production of platform chemicals, with emphasis on the Asia-Pacific region.

AbstractAlthough the activated sludge process, one of the most remarkable engineering inventions in the 20th century, has made significant contribution to wastewater reclamation in the past 100 years, its high energy consumption is posing a serious impact and challenge on the current wastewater industry worldwide and is also inevitably linked to the issue of global climate change. In this study, we argued that substantial improvement in the energy efficiency might be no longer achievable through further optimization of the activated sludge process. Instead, we should devote more effort to the development or the adoption of novel treatment configurations and emerging technologies. Of which an example is A-B process which can significantly improve the energy recovery potential at A-stage, while markedly reduces energy consumption at B-stage. Various configurations of A-B process with energy analysis are thus discussed. It appears highly possible to achieve an overall energy gain in WWTPs with A-B process as a core.

Batch assays are currently used to study the kinetic behavior of microbial growth. However, it has been shown that the outcome of batch experiments is greatly influenced by the initial ratio of substrate concentration (S(o)) to biomass concentration (Xo). Substrate-sufficient batch culture is known to have mechanisms of spilling energy that lead to significant nongrowth-associated substrate consumption, and the Monod equation is no longer appropriate. By incorporating substrate consumption associated with energy spilling into the balance of the substrate oxidation reaction, a kinetic model for the observed specific substrate consumption rate was developed for substrate-sufficient batch culture of activated sludge, and was further verified by experimental data. It was demonstrated that the specific substrate consumption rate increased with the increase of the S(o)/Xo ratio, and the majority of substrate was consumed through energy spilling at high S(o)/Xo ratios. It appears that the S(o)/Xo ratio is a key parameter in regulating metabolic pathways of microorganisms.

The conventional activated sludge (CAS) process has been widely employed for wastewater treatment for more than one hundred years. Recently, more and more concerns have been raised on the CAS process due to its high energy consumption and production of huge amount of waste activated sludge, which are inevitably linked to the issue of environmental sustainability and global climate change. Facing to such emerging and challenging situation, this study reported a novel A-B process in which an anaerobic moving bed biofilm reactor (AMBBR) served a lead A-stage for COD capture towards biogas production and an integrated fixed-biofilm and activated sludge sequencing batch reactor (IFAS-SBR) was employed as B-stage for biological nitrogen removal. Results showed that about 85% of wastewater COD was removed in the steady-state AMBBR with a total energy production rate of 0.28 kWh/m3 wastewater treated, while 85% of N-removal was achieved when the stable nitrite shunt was established in the IFAS-SBR. Moreover, 90% of dissolved methane in the AMBBR effluent could be removed by the proposed flash chamber at the lower energy demand of 0.12 kWh/m3 which could be offset by the potential energy harvested from produced methane. Compared to the CAS process, the production of waste sludge was reduced by about 75% in the proposed A-B process due to the efficient COD capture at the A-stage, leading to significant energy savings from aeration for COD oxidation and post-treatment of waste sludge at the B-stage. Consequently, this study offers in-depth insights into A-B process which should be considered as an ideal candidate for achieving the energy-neutral or even energy positive operation of a municipal wastewater treatment. Given the complex situation in A-B process, future study is needed to look into the system optimization towards the operational synergy between A- and B-stage in terms of energy recovery and nitrogen removal.

Globally increasing concerns have been raised on the high energy consumption and greenhouse gas emissions in conventional municipal wastewater treatment processes over the past decades. In this study, a self-sustaining synergetic microalgal-bacterial granular sludge process was thus developed to address these challenges. The results showed that the microalgal-bacterial granular sludge process was capable of removing 92.69%, 96.84% and 87.16% of influent organics, ammonia and phosphorus under non-aeration conditions over a short time of 6 h. The effluent could meet the increasingly stringent discharge standards in many countries worldwide. A tight synergetic interrelationship effect between microalgae and bacteria in granules was essential for such excellent process performance. The stoichiometric and functional genes analyses further revealed that most of organic matter and nutrients were removed through microalgal and bacterial assimilations. Moreover, it was found that there existed a desirable distribution of functional species of microalgae and bacteria in microalgal-bacterial granules, which appeared to be essential for the self-sustaining synergetic reactions and stability of microalgal-bacterial granules. Consequently, this work may offer a promising engineering alternative with great potential to achieve energy-efficient and environmentally sustainable municipal wastewater treatment.