Quanbao Zhao

Synthesis of Fe3O4/Polyacrylonitrile Composite Electrospun Nanofiber Mat for Effective Adsorption of Tetracycline.

Novel Fe3O4/polyacrylonitrile (PAN) composite nanofibers (NFs) were prepared by a simple two-step process, an electrospinning and solvothermal method. Characterization by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) demonstrated formation of a uniform nanoparticles coating (about 20 nm in thickness) on the PAN nanofiber backbone. The coating was constructed by well-crystallized cubic phase Fe3O4 nanoparticles as examined by X-ray diffraction spectroscopy (XRD). The coating doubled the specific surface area of NFs, from 8.4 to 17.8 m2 g(-1), as confirmed by nitrogen sorption isotherm analysis. To evaluate the feasibility of Fe3O4/PAN composite NFs as a potential adsorbent for antibiotic removal, batch adsorption experiments were conducted using tetracycline (TC) as the model antibiotic molecule. The results showed that Fe3O4/PAN composite NFs were effective in removing TC with no impactful loss of Fe in the pH regime of environmental interest (5-8). The adsorption of TC onto Fe3O4/PAN composite NFs better fitted the pseudo-second-order kinetics model, and the maximum adsorption capacity calculated from Langmuir isotherm model was 257.07 mg g(-1) at pH 6. The composite NFs also exhibited good regenerability over repeated adsorption/desorption cycles. Surface complexation between TC and the composite NFs contributed most to the adsorption as elucidated by X-ray photoelectron spectroscopy (XPS). This highly effective and novel adsorbent can be easily modularized and separated, promising its huge potential in drinking and wastewater treatment for antibiotic removal.

Efficient anaerobic digestion of whole microalgae and lipid-extracted microalgae residues for methane energy production

The primary aim of this study was to completely investigate extensive biological methane potential (BMP) on both whole microalgae and its lipid-extracted biomass residues with various degrees of biomass pretreatment. Specific methane productivities (SMP) under batch conditions for non-lipid extracted biomass were better than lipid-extracted biomass residues and exhibited no signs of ammonia or carbon/nitrogen (C/N) ratio inhibition when digested at high I/S ratio (I/S ratio⩾1.0). SMP for suitably extracted biomass ranged from 0.30 to 0.38LCH4/gVS (volatile solids). For both whole and lipid-extracted biomass, overall organic conversion ranged from 59.33 to 78.50 as a measure of %VS reduction with greater percentage biodegradability in general found within the lipid-extracted biomass. Higher production levels correlated to lipid content with a linear relationship between SMP and ash-free lipid content being developed at a R(2) of 0.814.

Enhancing volatile fatty acid (VFA) and bio-methane production from lawn grass with pretreatment

The bioconversion of fiber-based carbohydrates during anaerobic digestion (AD) is impeded due to the recalcitrant nature of the plant cell wall. Pretreatment of lignocellulose materials under mild conditions are needed to improve the digestibility at minimum cost. This study investigated the effects of different pretreatments, including ozone, soaking aqueous ammonia (SAA), combined ozone and SAA (OSAA), and size reduction to enhance volatile fatty acid (VFA) and bio-methane production when lawn grass was used as substrate. To study VFA production, methanogenesis was selectively inhibited by sodium 2-bromoethanesulfonate to decouple the relation between VFA and bio-methane. The enzymatic hydrolysis of SAA (residence time 24h at 50°C) and OSAA (10 min ozonation and 6h of SAA) in pretreatment of lawn grass sample resulted in 86.71% and 89.63% sugar recovery, respectively. The specific methane yields of the control, ozone, SAA, OSAA, and size-reduced grass samples were 402.5, 358.8, 481.0, 462.6, and 358.3 ml CH4/g volatile solid (VS), respectively.

Methanosarcina domination in anaerobic sequencing batch reactor at short hydraulic retention time

The Archaea population of anaerobic sequential batch reactor (ASBR) featuring cycle operations under varying hydraulic retention time (HRT) was evaluated for treating a dilute waste stream. Terminal-Restriction Length Polymorphism and clone libraries for both 16S rRNA gene and mcrA gene were employed to characterize the methanogenic community structure. Results revealed that a Methanosarcina dominated methanogenic community was successfully established when using an ASBR digester at short HRT. It was revealed that both 16S rRNA and mcrA clone library could not provide complete community structure, while combination of two different clone libraries could capture more archaea diversity. Thermodynamic calculations confirmed a preference for the observed population structure. The results both experimentally and theoretically confirmed that Methanosarcina dominance emphasizing ASBRs important role in treating low strength wastewater as Methanosarcina will be more adept at overcoming temperature and shock loadings experienced with treating this type of wastewater.

Kinetics of psychrophilic anaerobic sequencing batch reactor treating flushed dairy manure.

In this study, a new strategy, improving biomass retention with fiber material present within the dairy manure as biofilm carriers, was evaluated for treating flushed dairy manure in a psychrophilic anaerobic sequencing batch reactor (ASBR). A kinetic study was carried out for process control and design by comparing four microbial growth kinetic models, i.e. first order, Grau, Monod and Chen and Hashimoto models. A volumetric methane production rate of 0.24L/L/d of and a specific methane productivity of 0.19L/gVSloaded were achieved at 6days HRT. It was proved that an ASBR using manure fiber as support media not only improved methane production but also reduced the necessary HRT and temperature to achieve a similar treating efficiency compared with current technologies. The kinetic model can be used for design and optimization of the process.

Experimental and modeling study of a two-stage pilot scale high solid anaerobic digester system.

This study established a comprehensive model to configure a new two-stage high solid anaerobic digester (HSAD) system designed for highly degradable organic fraction of municipal solid wastes (OFMSW). The HSAD reactor as the first stage was naturally separated into two zones due to biogas floatation and low specific gravity of solid waste. The solid waste was retained in the upper zone while only the liquid leachate resided in the lower zone of the HSAD reactor. Continuous stirred-tank reactor (CSTR) and advective-diffusive reactor (ADR) models were constructed in series to describe the whole system. Anaerobic digestion model No. 1 (ADM1) was used as reaction kinetics and incorporated into each reactor module. Compared with the experimental data, the simulation results indicated that the model was able to well predict the pH, volatile fatty acid (VFA) and biogas production.

Analysis and optimization of ammonia stripping using multi-fluid model

Ammonia recovery from anaerobic digestion (AD) is a notably beneficial process for removing excess nitrogen, producing low cost fertilizer and enhancing odor abatement. A process was developed for nutrients recovery by integrating a simple and effective stripping process with AD system. To design, optimize and scale up this system, multi-fluid model was developed to simulate flow, mass transfer and reactions in the ammonia stripping tower. The mass and heat transfer and dissociation reactions were introduced into the CFD framework. The air/liquid ratio in each cell of the domain was considered in heterogeneous mass transfer rate. Good agreement between CFD modeling and experiments employing a packed bed was obtained on the effect of pH and temperature upon ammonia removal. It was found that the liquid to gas mass transfer rate became slower at the lower part of the packed bed with high air/liquid ratio and short liquid resident time, decreasing ammonia removal efficiency. The predicted contours at the lower part also showed decreases in liquid volume fraction and liquid temperature. These results suggest a great potential compensation to use the multi-section feed-in and recirculation for improving reactor performance.

The Selective Removal of H2S over CO2 from Biogas in a Bubble Column Using Pretreated Digester Effluent

Abstract. Raw biogas purification can be achieved using various physicochemical techniques. Unfortunately, techniques for the simultaneous absorption of CO2 and H2S are susceptible to the corrosive nature of H2S. Furthermore, the absorbents utilized are often expensive, thus requiring regeneration. Concurrently, on farm digesters are now moving towards the incorporation of NH3 recovery. One such process, air stripping, requires elevation of pH and production of an alkaline effluent. Therefore, a physicochemical H2S removal process was investigated in a bubble column reactor using this alkaline absorbent. Selective removal of H2S over CO2 increased nearly 50% by altering the sparger configuration. Further selectivity was achieved by decreasing the effluent height in the bubble column and increasing the superficial gas velocity. Continuous countercurrent mode of operation was tested and relatively high H2S removal efficiency (84%) was achieved at a biogas‑to‑effluent ratio (v/v) of 20:1, close to that typically found on digesters.

Enhance volatile fatty acid (VFA) and bio-methane productivity by pretreatment of lawn grass

Abstract. Lawn grass is a huge potential source of bio-fuel production because there are 27.6 million acres of turf grass in U.S., and 21 million acres in home lawns. Anaerobic digestion (AD) of lawn grass is an effective way to produce bio-methane, and to reduce the strain on the environment from greenhouse gases and overcrowded landfills. The potential bioconversion of carbohydrates in this potential resource, however, is limited by the associated cellulose and hemicellulose within the grass fiber. These constitutes must be broken down into their corresponding monomers (sugars), so that microorganisms can efficiently utilize them. To establish an efficient AD system, three pretreatments including ozone, soaking aqueous ammonia (SAA), and a combination of ozone and soaking aqueous ammonia (OSAA) optimized in our group were investigated to enhance volatile fatty acid (VFA) and bio-methane productivity of Kentucky bluegrass (Poa pratensis L.). Sodium 2-bromoethanesulfonate was used to inhibit methanogenic bacteria for studying VFA production. The results showed that the ammonia pretreatment was the most effective way to accelerate VFA and bio- methane production rate of kentucky bluegrass. These results would suggest that aqueous ammonia reused from our developed nutrient recovery system will reduce the cost of pretreatment.