The short- and long-term inhibitory effects of Fe (II) on anaerobic ammonium oxidizing (anammox) process.

The application of the anammox process has great potential in treating nitrogen-rich wastewater. The presence of Fe (II) is expected to affect the growth and activity of anammox bacteria. Short-term (acute) and long-term effects (chronic) of Fe (II) on anammox activity were investigated. In the short-term study, results demonstrated that the optimum concentration of Fe (II) that could be added to anammox is 0.08 mM, at which specific anammox activity (SAA) improved by 60% compared to the control assay, 0.00 mM. The inhibition concentration, IC50, of Fe (II) was found to be 0.192 mM. Kinetics of anammox specific growth rate were estimated based on results of the batch test and evaluated with Han-Levenspiel's substrate inhibition kinetics model. The optimum concentration and IC50 of Fe (II) predicted by the Han-Levenspiel model was similar to the batch test, with values of 0.07 mM and 0.20 mM, respectively. The long-term effect of Fe (II) on the performance of a sequencing batch reactor (SBR) was evaluated. Results showed that an appropriate Fe (II) addition enhanced anammox activity, achieving 85% NH4 +-N and 96% NO2 --N removal efficiency when 0.08 mM of Fe (II) was added. Quantitative polymerase chain reaction (qPCR) was adopted to detect and identify the anammox bacteria.

Salinity-driven heterogeneity toward anammox distribution and growth kinetics.

Anaerobic ammonium oxidation (anammox) has been widely applied for biological nitrogen removal in freshwater systems, and there is a potential for its extension in saline water systems. In this study, the abundance and biodiversity of anammox bacteria were investigated in both saline and freshwater full-scale sewage treatment plants (STPs). The anammox bacteria were widely found in four tested STPs with abundance of 105-107 copies per mL of 16S rRNA gene. Phylogenetic results showed that Ca. Scalindua and Ca. Brocadia dominated in saline and freshwater STPs, respectively. Ca. Kuenenia dominated in one of freshwater STPs. However, redundancy discriminate analysis (RDA) indicates the distribution of Ca. Kuenenia in both saline and freshwater conditions. To further elucidate these observations, the Monod model was integrated with Gauss equation for the evaluation of salinity-induced kinetics. Model results reveal that when nitrite concentration (SNO2-) is higher than nitrite affinity constant (KNO2-), salinity (over ~ 3.0%) is responsible for Candidatus Scalindua dominance over Candidatus Kuenenia. Conversely, in nitrite-depleted conditions (KNO2- ≥ SNO2-), high nitrite affinity leads to the predominance of Ca. Scalindua in all salinities. This study provides fundamental insights into saline anammox applications.

Multi-agent simulation regulated by microbe-oriented thermodynamics and kinetics equations for exploiting interspecies dynamics and evolution between methanogenesis, sulfidogenesis, hydrogenesis and exoelectrogenesis.

Multi-agent simulation (MAS) regulated by microbe-oriented thermodynamics and kinetics equations were performed for exploiting the interspecies dynamics and evolution in anaerobic respiration and bioelectrochemical systems. A newly-defined kinetically thermodynamic parameter is recognized microbes as agents in various conditions, including electron donors and acceptors, temperature, pH, etc. For verification of the MAS, the treatment of synthetic wastewater containing glucose and acetate was evaluated in four 25°C laboratory-scale reactors with different electron acceptors and cathode materials that had potential for methanogenesis, hydrogenesis, sulfidogenesis and exoelectrogenesis. Within 1000 h operation, the reactors performance and microbial structures using 16S rRNA sequencing matched with the MAS, suggesting acetoclastic exoelectrogenesis predominance (Geobacter). After 2400 h, MAS observed the co-existence of acetoclastic methanogenesis and acetoclastic and propionate exoelectrogenesis, as was reported previously. Such microbial evolution from the short-term to long-term operation likely resulted from the glucose-driven propionate. The MAS developed is applicable in a wide range of complex engineering and natural ecosystems.

Mathematical model to appraise the inhibitory effect of phenolic compounds derived from lignin for biobutanol production.

This study aimed to establish a mathematical modeling to evaluate the inhibitory effect of phenolic derivatives on acetone-butanol-ethanol (ABE) fermentation by Clostridium saccharoperbutylacetonicum N1-4. Vanillin, 4-hydroxybenzoic acid, and syringaldehyde were selected to represent guaiacyl, hydroxyphenyl, and syringyl phenols, respectively, to be examined in a series of fed-batch experiments. Results show the presence of phenolic derivatives blocked the pathway of the assimilation of organic acids and reduced cell growth and glucose utilization. The inhibition model projected that the levels of 0.13, 0.14, and 0.04 g L-1 for vanillin, 4-hydroxybenzoic acid, and syringaldehyde, respectively, resulted in 25% inhibition of butanol production, whereas 100% inhibition was predicted at the levels of 4.94, 4.37, and 4.20 g L-1 for vanillin, 4-hydroxybenzoic acid, and syringaldehyde, respectively. Syringaldehyde was more toxic than the other two compounds. The established model described that the phenolic compounds derived from different phenyl propane monomers of lignin severely obstructed biobutanol production.

A review on the bioenergetics of anaerobic microbial metabolism close to the thermodynamic limits and its implications for digestion applications.

The exploration of the energetics of anaerobic digestion systems can reveal how microorganisms cooperate efficiently for cell growth and methane production, especially under low-substrate conditions. The establishment of a thermodynamically interdependent partnership, called anaerobic syntrophy, allows unfavorable reactions to proceed. Interspecies electron transfer and the concentrations of electron carriers are crucial for maintaining this mutualistic activity. This critical review summarizes the functional microorganisms and syntroph partners, particularly in the metabolic pathways and energy conservation of syntrophs. The kinetics and thermodynamics of propionate degradation to methane, reversibility of the acetate oxidation process, and estimation of microbial growth are summarized. The various routes of interspecies electron transfer, reverse electron transfer, and Poly-ß-hydroxyalkanoate formation in the syntrophic community are also reviewed. Finally, promising and critical directions of future research are proposed. Fundamental insight in the activities and interactions involved in AD systems could serve as a guidance for engineered systems optimization and upgrade.

Study of chemical pretreatment and enzymatic saccharification for producing fermentable sugars from rice straw.

This study evaluated a cost-effective approach for the conversion of rice straw into fermentable sugars. The composition of rice straw pretreated with 1 % sulfuric acid or 1 % sodium hydroxide solution was compared to rice straw with no chemical pretreatment. Enzymatic saccharification experiments on non-pretreated rice straw (NPRS), pretreated rice straw (PRS), and pretreated rice straw with acid hydrolysate (PRSAH) were conducted in a series of batch reactors. The results indicated that pretreating the rice straw with dilute acid and base increased the cellulose content from 38 % to over 50 %. During enzymatic saccharification, straight aliphatic cellulose was hydrolyzed before branched hemicellulose, and glucose was the major hydrolysis product. The glucose yield was 0.52 g glucose/g for NPRS and was comparable to the yields of 0.50 g glucose/g for PRS and 0.58 g glucose/g for PRSAH. The hydrolysis of rice straw to produce glucose can be described by a first-order reaction with a rate constant of 0.0550 d(-1) for NPRS, 0.0653 d(-1) for PRSAH, and 0.0654 d(-1) for PRS. Overall, the production of fermentable sugars from ground rice straw will be more cost effective if the straw is not pretreated with chemicals.

Evaluation of recycling the effluent of hydrogen fermentation for biobutanol production: kinetic study with butyrate and sucrose concentrations.

Butyrate in the effluent of hydrogen-producing bioreactor is a potential feed for biobutanol production. For recycling butyrate, this study investigated the kinetics of biobutanol production by Clostridium beijerinckii NRRL B592 from different paired concentrations of butyrate and sucrose in a series of batch reactors. Results show that the lag time of butanol production increased with higher concentration of either sucrose or butyrate. In regression analyses, the maximum specific butanol production potential of 6.49 g g(-1) of dry cell was projected for 31.9 g L(-1) sucrose and 1.3 g L(-1) butyrate, and the maximum specific butanol production rate of 0.87 g d(-1) g(-1) of dry cell was predicted for 25.0 g L(-1) sucrose and 2.6 g L(-1) butyrate. The specific butanol production potential will decrease if more butyrate is added to the reactor. However, both sucrose and butyrate concentrations are weighted equally on the specific butanol production rate. This observation also is true on butanol yield. The maximum butanol yield of 0.49 mol mol(-1) was projected for 25.0 g L(-1) sucrose and 2.3 g L(-1) butyrate. In addition, a confirmation study found butanol yield increased from 0.2 to 0.3 mol mol(-1) when butyrate addition increased from 0 to 1 g L(-1) under low sugar concentration (3.8 g L(-1) sucrose). The existence of butyrate increases the activity of biobutanol production and reduces the fermentable sugar concentration needed for acetone-butanol-ethanol fermentation.

Thermophilic bioleaching of heavy metals from waste sludge using response surface methodology.

The bioleaching process is considered to be more efficient and environmentally friendly than conventional technologies for removal of heavy metals from waste sludge. The objective of this study was to develop an optimal thermophilic bioleaching process for the treatment of waste sludge containing high concentrations of heavy metals. In this study, two operating parameters, sludge solid content and sulfur (substrate) concentration, were studied based on a central composite design (CCD) for their metal solubilization and solid degradation performances. The optimal bioleaching operation conditions were then determined using the response surface methodology (RSM). The results indicated that an increase in sludge solid content range from 0.5% to 5.0% resulted in a decrease in the pH reduction rate due to the increase in buffering capacity. The rate of acidification corresponded to sulfur concentration until sulfur itself became inhibitory. At sulfur concentration beyond approximately 2.75%, the lower acidification rate was caused by a lower bacteria growth rate. Similar trends were also observed in the variations of ORP and sulfate concentrations during this thermophilic bioleaching process. At the optimum conditions of a sludge solid content of 0.5% and sulfur concentration of 2.5%, the thermophilic bioleaching process achieved the maximum solubilization of 97%, 99%, 99% and 78% for Cu, Zn, Ni and Pb, respectively. At the same time, the maximum SS and VSS destruction efficiency were 69% and 63%, respectively.

Evaluation of biobutanol production from non-pretreated rice straw hydrolysate under non-sterile environmental conditions.

The study aims to investigate a cost-effective approach to convert non-pretreated rice straw hydrolysate into biobutanol. The influences of the initial cell concentration and incubation temperature on biobutanol production were evaluated under both sterile and non-sterile conditions. Results indicate that 100% glucose utilization could be achieved for initial cell concentrations greater than 2100 mg/L under both sterile and non-sterile conditions. Regression analyses resolve that under the sterile condition, the maximum butanol productivity of 1.45 g/L/d was projected at 1.96 g/L of cells and 32.3 °C, while the maximum butanol yield of 0.22 g/g was predicted at 2.01 g/L of cells and 26.3 °C. These two maximum values could not be projected by the regression analyses for the non-sterile condition. However, this study confirms that a high initial cell concentration of Clostridium saccharoperbutylacetonicum N1-4 can minimize interference from other microbes so that non-sterile biobutanol production is comparable to sterile biobutanol production.

Biohydrogen production in continuous-flow reactor using mixed microbial culture.

The goal of the proposed project was to develop an anaerobic fermentation process that converts negative-value organic wastes into hydrogen-rich gas in a continuous-flow reactor under different operating conditions, such as hydraulic retention time (HRT), heat treatment, pH, and substrates. A series of batch tests were also conducted in parallel to the continuous study to evaluate the hydrogen conversion efficiency of two different organic substrates, namely sucrose and starch. A heat shock (at 90 degrees C for 15 minutes) was applied to the sludge in an external heating chamber known as a sludge activation chamber, as a method to impose a selection pressure to eliminate non-spore-forming, hydrogen-consuming bacteria and to activate spore germination. The experimental results showed that the heat activation of biomass enhanced hydrogen production by selecting for hydrogen-producing, spore-forming bacteria. The batch feeding at a shorter HRT of 20 hours (or higher organic loading rate) favored hydrogen production, whereas, at a longer HRT of 30 hours, methane was detected in the gas phase. The major organic acids of hydrogen fermentation were acetate, butyrate, and propionate. Up to 23.1% of influent chemical oxygen demand was consumed in biomass synthesis. Batch tests showed that the hydrogen-production potential of starch was lower than sucrose, and better conversion efficiency from starch was obtained at a lower pH of 4.5. However, addition of sucrose to starch improved the overall hydrogen-production potential and hydrogen-production rate. This study showed that sustainable biohydrogen production from carbohydrate-rich substrates is possible through heat activation of settled sludge.