The impact of different operating conditions on membrane fouling and EPS production

The main goal of this research was to investigate how different factors influence membrane fouling. The impact of the different concentrations of activated sludge and the amount of extracellular polymer substances (EPS) were monitored. Two pilot plants with submerged membrane modules (hollow fiber and flat sheet) were operated and the raw wastewater was used.Humic substances were identified as the major components of EPS in the activated sludge (more than 34%) in both pilot plants. As the basic constituent in permeate, humic substances were identified as the most dominant components in the effluent (61%) in both pilot plants. Conversely, proteins were mostly analyzed in permeate and supernatant below the detection limit. The total amount of EPS [mg g⁻¹ (VSS)] was similar for concentrations of activated sludge 6, 10 and 14 g L⁻¹. Carbohydrates were identified as the component of EPS which tends most to clog membranes.     

Hydrodynamic behaviors in fermentative hydrogen bioreactors by pressure fluctuation analysis

Three bioreactor configurations were employed in these investigations, which consisted of working volumes of 10, 1.2 and 1.2 L. Power spectrum diagrams of bed pressure fluctuation were used with hydraulic retention times (HRT) and geometric factors to identify the flow regimes in the bioreactors, where HRT varied from 8 to 1 h. It was found that the flow regimes in the bioreactors changed from a dispersed regime to coalesced and slugging regimes, when the biogas production rate (BPR) increased, as a result of decreasing the operating HRT. The flow regime was a dispersed bubble regime when the HRT was higher than 4 h in the bioreactor, whereas when the HRT was 2 h the coalesced bubble phenomena occurred in the bioreactor. A slugging regime was found when the HRT was lower than 1 h in thinner bioreactor.     

State of the art of aerobic granulation in continuous flow bioreactors

In the wake of the success of aerobic granulation in sequential batch reactors (SBRs) for treating wastewater, attention is beginning to turn to continuous flow applications. This is a necessary step given the advantages of continuous flow treatment processes and the fact that the majority of full-scale wastewater treatment plants across the world are operated with aeration tanks and clarifiers in a continuous flow mode. As in SBRs, applying a selection pressure, based on differences in either settling velocity or the size of the biomass, is essential for successful granulation in continuous flow reactors (CFRs). CFRs employed for aerobic granulation come in multiple configurations, each with their own means of achieving such a selection pressure. Other factors, such as bioaugmentation and hydraulic shear force, also contribute to aerobic granulation to some extent. Besides the formation of aerobic granules, long-term stability of aerobic granules is also a critical issue to be addressed. Inorganic precipitation, special inocula, and various operational optimization strategies have been used to improve granule long-term structural integrity. Accumulated studies reviewed in this work demonstrate that aerobic granulation in CFRs is capable of removing a wide spectrum of contaminants and achieving properties generally comparable to those in SBRs. Despite the notable research progress made toward successful aerobic granulation in lab-scale CFRs, to the best of our knowledge, there are only three full-scale tests of the technique, two being seeded with anammox-supported aerobic granules and the other with conventional aerobic granules; two other process alternatives are currently in development. Application of settling- or size-based selection pressures and feast/famine conditions are especially difficult to implement to these and similar mainstream systems. Future research efforts needs to be focused on the optimization of the granule-to-floc ratio, enhancement of granule activity, improvement of long-term granule stability, and a better understanding of aerobic granulation mechanisms in CFRs, especially in full-scale applications.     

Recovery strategies for tackling the impact of phenolic compounds in a UASB reactor treating coal gasification wastewater

The impact of phenolic compounds (around 3.2 g/L) resulted in a completely failed performance in a mesophilic UASB reactor treating coal gasification wastewater. The recovery strategies, including extension of HRT, dilution, oxygen-limited aeration, and addition of powdered activated carbon were evaluated in batch tests, in order to obtain the most appropriate way for the quick recovery of the failed reactor performance. Results indicated that addition of powdered activated carbon and oxygen-limited aeration were the best recovery strategies in the batch tests. In the UASB reactor, addition of powdered activated carbon of 1 g/L shortened the recovery time from 25 to 9 days and oxygen-limited aeration of 0-0.5 mgO₂/L reduced the recovery time to 17 days. Reduction of bioavailable concentration of phenolic compounds and recovery of sludge activity were the decisive factors for the recovery strategies to tackle the impact of phenolic compounds in anaerobic treatment of coal gasification wastewater.     

Stimulation of bioprocesses by ultrasound

Ultrasound (US) has become a ubiquitous technological process in a large variety of scientific disciplines. However, little information exists on the use of ultrasound to enhance biological processes and/or processing and consequently this paper provides an overview of work reported to date on this topic. This review provides a brief introduction to ultrasound and the history of ultrasound as applied to bioprocesses. This is followed by a discussion of the influence of US on discrete enzyme systems, enzymes used in bioremediation, microbial fermentations and enzymatic hydrolysis of biopolymers. Augmentation of anaerobic digestion by US is then considered along with enhancement of enzymes in food science and technology. The use of ultrasonically stimulated enzymes in synthesis is then considered and other relevant miscellaneous topics are described. It is concluded that the precise mechanism of action of US in bio-processing remains to be elucidated though a variety of plausible suggestions are made.     

Aerobic granular sludge: recent advances

Aerobic granulation, a novel environmental biotechnological process, was increasingly drawing interest of researchers engaging in work in the area of biological wastewater treatment. Developed about one decade ago, it was exciting research work that explored beyond the limits of aerobic wastewater treatment such as treatment of high strength organic wastewaters, bioremediation of toxic aromatic pollutants including phenol, toluene, pyridine and textile dyes, removal of nitrogen, phosphate, sulphate and nuclear waste and adsorption of heavy metals. Despite this intensive research the mechanisms responsible for aerobic granulation and the strategy to expedite the formation of granular sludge, and effects of different operational and environmental factors have not yet been clearly described. This paper provides an up-to-date review on recent research development in aerobic biogranulation technology and applications in treating toxic industrial and municipal wastewaters. Factors affecting granulation, granule characterization, granulation hypotheses, effects of different operational parameters on aerobic granulation, response of aerobic granules to different environmental conditions, their applications in bioremediations, and possible future trends were delineated. The review attempts to shed light on the fundamental understanding in aerobic granulation by newly employed confocal laser scanning microscopic techniques and microscopic observations of granules.     

Comparative study of the effect of ultrasonication on the anaerobic biodegradability of food waste in single and two-stage systems

Five different mesophilic systems were evaluated in this study for the anaerobic treatment of food waste. Systems A and B were one stage methane with unsonicated and sonicated feeds, respectively, while, systems C and D were two-stage hydrogen and methane with unsonicated and sonicated feeds, respectively. System E comprised a novel sonicated biological hydrogen reactor (SBHR) followed by methane reactor. The results showed that sonication inside the reactor in the first stage (system E) showed superior results compared to all other systems. Overall VSS removal efficiencies of 67%, 59%, 51%, 44%, and 36% were achieved in systems E, D, C, B, and A, respectively. Volumetric hydrogen production rates of 4.8, 3.3, and 2.6 L H₂/L_reactor d were achieved in the SBHR, CSTR with and without sonicated feed, respectively, while, methane production rates of 1.6, 2.1, 2.3, 2.6, and 3.2 L CH₄/L_reactor d were achieved in systems A-E, respectively.     

Full-loop operation and cathodic acidification of a microbial fuel cell operated on domestic wastewater

The present study emphasizes the importance of overcoming proton limitation in a microbial fuel cell operated on domestic wastewater. When the anode-treated effluent was allowed to trickle into the cathodic compartment (full-loop operation), high COD and suspended solids removal efficiencies over 75% and 84%, respectively, were achieved while ensuring substantial and sustainable power generation. Lower removal efficiencies resulted in decreased cell electromotive force caused by excess substrate crossover. By decreasing the pH in the cathodic compartment to values below 2, we were able to further increase the maximum power generation by 180% in batch mode and 380% in continuous mode as compared to a negative control (tap water of pH 7.6). Under the optimized conditions, the internal resistance and electromotive force were 11 Ω and 0.6 V, respectively, which correspond to the state of the art.     

Pre-treatments to enhance the biodegradability of waste activated sludge: Elucidating the rate limiting step

Pre-treatments for waste activated sludge (WAS) are, in most cases, an attempt to increase the biodegradation and/or improve hydrolysis rate of WAS after anaerobic digestion. This review presents an extensive analysis of WAS pre-treatments effectiveness focusing on increasing the biodegradability. In the first part of the review, WAS is considered as a cluster of organic components: proteins, carbohydrates, humic substances and cells. Based on this breakdown into components, the effect of different pre-treatments on each component (and in combination) is described. Also, possible reasons for the contradictory results frequently found among different studies dealing with the same pre-treatment are included. In the second part, the review describes the effects on volatile solids removal by digestion after pre-treatment and on the dewaterability of the final digestate. The energy balance and potential limiting factors for each pre-treatment are also taken into account. From the published works it is concluded that some pre-treatment techniques, such as thermal hydrolysis, thermal phased anaerobic digestion and low-temperature pre-treatment are effective ways to increase energy production and to improve other sludge properties, such as dewatering. However, these techniques are very energy intensive and require a large capital outlay, so research on milder pre-treatment techniques is valuable.     

CO2点阵激光联合湿润烧伤膏对创伤性瘢痕的疗效分析

目的:探讨CO_2点阵激光联合湿润烧伤膏治疗创伤性瘢痕的临床疗效。方法:选取73例创伤性瘢痕患者,年龄21-35岁,对照组(35例)给予CO_2点阵激光术治疗,术后涂抹莫匹罗星软膏护理,观察组(38例)采用CO_2点阵激光术联合湿润烧伤膏治疗。通过对患者治疗后3个月的体征、疗效及3个月内不良反应的发生情况评价CO_2点阵激光术联合湿润烧伤膏对创伤性瘢痕的疗效。结果:与治疗前相比,两组治疗后3个月的VSS评分均明显提高(P0.05),但两组间VSS评分相比差异没有统计学意义(P0.05)。治疗后3个月,观察组的治疗有效率明显高于对照组(P0.05),治疗后3个月期间,观察组的不良反应发生率明显低于对照组(P0.05),色素沉积和创面感染是主要的不良反应症状。结论:CO_2点阵激光技术联合润湿烧伤膏对于创伤性瘢痕具有良好的治疗效果,且安全性高。