Semi-continuous Mode Of Operation Research Articles

Valorization of organic carbon in primary sludge via semi-continuous dark fermentation: First step to establish a wastewater biorefinery

In this study, lab-scale, bench-scale, and pilot-scale experiments were carried out to optimize short-chain fatty acids production from primary sludge. Batch tests showed the requirement of short retention times and semi-continuous operation mode showed a plateau of maximum daily productivity at 36-hours hydraulic retention time with minimal methanation. Optimization from pH 5 to pH 10 at 36 h-hydraulic retention time under long-term semi-continuous operating mode revealed that production of short-chain fatty acids was pH dependent and highest yields could be achieved at pH 7 by establishing optimum redox conditions for fermentation. Pilot-scale experiments at 32 °C showed that daily productivity (3.1 g∙Lreactor-1∙dHRT-1) and yields (150 mg∙gVS-1; OLR = 21 gVS∙Lreactor-1∙dHRT-1; pH 7) of short-chain fatty acids could be significantly improved, specifically for acetic and propionic acids. From these results, a robust dark fermentation step for recovery of valuable products from the solids treatment step in a biorefinery can be achieved.

Electrocoagulation Technique for Treating Swine Slaughterhouse Wastewater from Batch to Semicontinuous Operation Mode

In this study, industrial swine slaughterhouse wastewater was treated by electrocoagulation process using batch and semicontinuous operation systems. Electrochemical technique was carried out in batch operation mode during 2.5 h applying different current densities in sulfate and chloride media. After finding the best operating parameters in batch mode (lab-scale), the process was transferred to a semicontinuous pre-pilot scale process using a filter-press FM01-LC type electrochemical reactor fitted with flat plate aluminum electrodes. In this stage, distinct current densities and mean linear flow rates were assessed.Total organic carbon, chemical oxygen demand, total phosphorus, total nitrogen, and potassium among other parameters were analyzed during both treatments. The industrial swine slaughterhouse wastewater contained TOC 333 mg L–1, COD 1765 mg L–1, TP 13.55 mg L–1, TN 327 mg L–1, K 45 mg L–1, turbidity 102 NTU, color –absorbance 0.90 A.U. at 415 nm–, conductivity 1.9 mS cm–1, and pH 6.9. The highest TOC removal efficiency (72.7%), in semicontinuous process, was found at j = 25 mA cm-2 and ur = 0.64 cm s-1 with an energy consumption of 19.80 kW h m-3. Residual COD and TP concentrations met the international standard limits. Moreover, complete discoloration and disinfection were achieved. EDXRF, SEM, EDAX, XRD, and FTIR analyzes indicate pollutants were removed by adsorption on aluminum/iron hydroxides/oxyhydroxides.

Sustainable Biodiesel Production by Transesterification of Waste Cooking Oil and Recycling of Wastewater Rich in Glycerol as a Feed to Microalgae

The amount of solid and liquid organic waste and wastewater is continuously increasing all over the world. The necessity of their reuse and recycling is, therefore, becoming more and more pressing. Furthermore, the limited fossil fuel resources, in conjunction with the need to reduce greenhouse gas emissions, advocate the production of renewable fuels. In this work, we analyze a sustainable second-generation process to produce biodiesel by transesterification of waste cooking oil, coupled with a third-generation process in cascade for recycling the incoming wastewater. Since this latter is rich in glycerol, it is used as a feed for microalgae, from which oil can be extracted and added to the waste cooking oil to further produce biodiesel and close the cycle. We studied the influence of different factors like temperature, catalyst load, and reactants ratio on the kinetics of transesterification of the waste oil and estimated the kinetic parameters by different kinetic schemes. The obtained values of activation energies and pre-exponential factors at chosen conditions of T = 60 °C and catalyst load of 0.6% w/w in methanol are: Ea,direct = 35,661 J mol−1, Ea,reverse = 72,989 J mol−1, k0,direct = 9.7708 [dm3 mol−1]3 min−1, and k0,reverse = 24,810 [dm3 mol−1]3 min−1 for the global fourth-order reversible reaction scheme and Ea = 67,348 J mol−1 and k0 = 2.157 × 109 min−1 for the simplified pseudo-first-order irreversible reaction scheme; both in strong agreement with literature data. Furthermore, we designed very efficient conditions for discontinuous and continuous operating mode, both at lab-scale and pilot-scale. The quality of the biodiesel produced from waste cooking sunflower oil is compared with that of biodiesel produced by different kinds of virgin vegetable oils, showing that the former possesses acceptable quality standards (Cetane number = 48 and LHV = 36,600 kJ kg−1). Finally, the recycling of wastewater rich in glycerol as a nutrient for mixotrophic microalgae nurturing is discussed, and microalgae growing kinetics are evaluated (k1 about 0.5 day−1), endorsing the possibility of algae extraction each 4–5 days in a semi-continuous operating mode. The experimental results at the pilot scale finally confirm the quality of biodiesel, and the obtained yields for a two-stage process prove the competitiveness of this sustainable process on the global market.

Effects of different antibiotic operation modes on anaerobic digestion of dairy manure: Focus on microbial population dynamics

The inhibition effect of four antibiotics, i.e. ampicillin (AMP), tylosin (TYL), florfenicol (FLO) and sulfamethazine (SMT), was investigated in dairy manure digesters for both single dosing and semi-continuous dosing operations over a period of 40 days. High throughput 16S rRNA sequence analysis revealed that dosing mode did have significant impact on microbial community, i.e. antibiotics had a notable effect on bacteria in single dosing digesters, while archaea were the major population affected in the semi-continuous dosing operations. FLO shows the most severe inhibition on biogas production and remarkably effected bacterial communities, which led to a complete upset of the whole community. Although the effect of SMT on biogas production was marginal, methanogens populations were notably shifted. A four-stage inhibition process on microbial community was proposed based on the ratio of the affected bacteria to archaea to shed new light on microbial population dynamics during anaerobic digestion. Moreover, we found that the semi-continuous operation mode of antibiotics is more efficient in terms of microbial community changes, which may guide the formulation of veterinary drug doses and cycle intervals.

Using seawater-based Na2CO3 medium for scrubbing the CO2 released from Bio-CNG plant for enhanced biomass production of Pseudanabaena limnetica

The concentration of CO2, one of the most important greenhouse gases (GHG), has reached to 409.8 ± 0.1 ppm in 2019. Although there are many carbon capture and storage (CCS) methods, they are very costly and their long term use raises concern about environmental safety. Alternatively, bio-sequestration of CO2 using microalgal cell factories has emerged as a promising way of recycling CO2 into biomass via photosynthesis. In the present study, Indigenous algal strain Pseudanabaena limnetica was cultivated in pneumatically agitated 60-L flat-panel photobioreactor system. The gas was released from Bio-CNG plant as by-product into Na2CO3-rich medium and cultivated in semicontinuous mode of operation. It was observed that when CO2 was sparged in seawater-based 0.02 M Na2CO3 solution, maximum CO2 was dissolved in the system and was used for algal cultivation. Control system produced 0.64 ± 0.035 g/L of biomass at the end of 15 days, whereas CO2 sparged Na2CO3 medium produced 0.81 ± 0.046 g/L of biomass. When CO2 from Bio-CNG station was fed, it resulted in biomass production of 1.62 ± 0.070 g/L at the end of 18 days compared to 1.46 ± 0.066 g/L of biomass produced in control system which was not fed with gas released from Bio-CNG plant as by-product. Thus, feeding CO2 directly into Na2CO3 medium and operating the system semicontinuously would be efficient for scrubbing CO2 from commercial Bio-CNG plant. This study proves that feeding CO2 gas from Bio-CNG plant into Na2CO3-rich alkaline system can be used to feed algae for enhanced biomass production.

Semifluidized Bed Adsorption Column Studies for Simultaneous Removal of Aqueous Phase Pb2+ and Cd2+ by Composite Adsorbents: an Experimental and Mass Transfer Dynamic Model–Based Approach

In this present work, the performance of a semifluidized bed adsorption column has been evaluated for the removal of Pb2+ and Cd2+ in a semi-continuous mode. The composite adsorbents have been synthesized from waste biomass–based biochar and alginate-based biopolymer. Synthesized adsorbent characterized and finally tested its effectiveness in the removal of both Pb2+ and Cd2+ metal ions by batch and semifluidized bed column adsorption studies. The adsorptive removal efficiencies were found to be dependent on solution pH, initial metal ion concentration, adsorbent dose or initial bed height, static bed height, system temperature and inlet flow rate of semifluidized bed operation. Pseudo-second-order kinetic model was fitted to the batch adsorption experimental data by non-linear and linear regression method and it was found that the non-linear method gives a better way of obtaining the various kinetic parameters and its applicability. A solute phase mass transfer–based dynamic model has been developed to explain the adsorptive behaviour of metal ions onto adsorbents during the semi-continuous mode of operation of a semifluidized bed system. Various mass transfer parameters and degree of dispersion coefficients for the individual packed and fluidized section were obtained from the developed model.

Environmental electroactive consortia as reusable biosensing element for freshwater toxicity monitoring

The development of tools to monitor water quality is mandatory in a scenario where clean water resources are decreasing. Here, the biosensing capability of an electroactive river sediment consortium was tested towards three model contaminants (glutaraldehyde, nickel(II) and chromium(III)). The proposed biosensor is a small membrane-less single chamber Microbial Fuel Cell (MFC), fabricated by 3D printing. Its semi-continuous mode of operation resulted in long-term current profile stability and reproducibility. A linear trend of response was obtained for glutaraldehyde in a concentration range of 5–1000 ppm. After the recovery of the electroactive consortium activity, the MFC-based biosensors were shown to be sensitive towards Ni(II) and Cr(III), at concentrations above 2 mg L−1. To effectively analyze biosensor response, a novel algorithm was proposed, offering advantages for the realization of energy-saving protocols for MFC-biosensor data transmission. Implementation of the device and method, from laboratory test to real environment, can offer a low cost in situ system for detection of water contaminants.

Self-build packed-bed bioreactor for rapid and effective BOD estimation.

This work demonstrated a simple, low-cost, rapid, and effective biochemical oxygen demand (BOD) estimation system based on a packed-bed bioreactor that can be easily self-built on-site at a particular wastewater treatment plant for continuous monitoring of the influent and effluent. The use of natural microbial consortium that were collected from the target wastewater and immobilized on a cheap porous carrier simply by adhesion resulted in an acceptable accuracy of over 95%. The newly developed semi-continuous operating mode with peak-type signals was shown to be able to continuously estimate BOD at a high flow rate to overcome the flow dependence of the oxygen electrode, limit clogging issues, enhance the response time, and lower the limit of detection. The resulting packed-bed bioreactors could work continuously for 22h with a coefficient of variance (CoV) of only 1.8% or for 13h a day for several days with a maximum CoV of 1.4% and their response was observed to be stable over 80 consecutive measurements. They exhibited stable responses at a wide pH range of 6.5-8.5, which is also the recommended range for aerobic wastewater treatment, emphasizing the greater ease of use of natural microorganisms for BOD estimation.

Biodegradation of crude oil hydrocarbons by a newly isolated biosurfactant producing strain

New bacterial strain BN66 was isolated by selective enrichment, identified as Bacillus cereus and proved to degrade crude oil, together with biosurfactant synthesis. Free and cryogel immobilized Bacillus cereus cells were involved in a crude oil degradation process. The studied strain degraded 93% of the aliphatic fraction for 48 h. We immobilized cells in two types of cryogels synthesized from high molar mass polyacrylamide or acrylamide precursors and explored the degradation capability and possibility for re-use of the preparations. Reusability tests revealed that the oil degradation ability of immobilized cells was stable after 47 days (28 °C and shaker speed 120 rpm) and the degradation rate of immobilized cells was maintained at a high level up to the 20th cycle of operation. The matrices obtained from high molar mass polyacrylamide appeared to be more suitable due to their ability to keep the cells within the carrier. The cells immobilized in cryogels exhibited more effective degradation for 22 active cycles at semicontinuous mode of operation compared to only three cycles performed by free cells.

Assessment of Batch and Semi-continuous Anaerobic Digestion of Food Waste at Psychrophilic Range at Different Food Waste to Inoculum Ratios and Organic Loading Rates

At present, most studies have been focused on anaerobic digestion (AD) of food waste (FW) at temperatures above 35 °C. While AD of FW at psychrophilic temperature has been rarely reported, this may be a more economical procedure for municipal solid waste (MSW) management by reducing the organic fraction content and the corresponding environmental impact from its disposal. FW and inoculum have been characterized and AD of FW assays have been run for 12 weeks in accordance with VDI 4630. The effect of FW to inoculum ratio (FWIR) has been assessed in batch assays and the organic load rate (OLR) has been tested in semi-continuous operation mode. In addition, soluble chemical oxygen demand (SCOD) evolution has been periodically measured during all tests. Results showed an important reduction of specific methane yield (SMY) (up to 65%) when FWIR is increased (from 0.5 to 1.5) in batch tests while SCOD removal remains quite constant (approx. 90%). On the other hand, during semi-continuous operation SMY and SCOD removal have been highly reduced (up to approx. 70 and 73%) when OLR is increased (from 1 to 3 g_VS L−1 d−1). Despite the low SMY, the AD of FW at psychrophilic temperature is a feasible solution, especially at low organic loads. Therefore, it may be used in decentralized strategies for improving the MSW management. This operation mode reduces installation costs and reactor operation complexity at the same time decreases the SCOD of municipal waste stream.

Crystallization-Based Isolation of Pure Rutin from Herbal Extract of Sophora japonica L.

Crystallization-based isolation of rutin from a plant extracts of Sophora Japonica was studied. Solid-liquid phase equilibria of rutin were determined in methanol, ethanol and 2-propanol. Solvate formation and phase stability were investigated using X-ray powder diffraction and thermogravimetric analysis coupled with differential scanning calorimetry. The experiments revealed a short-term stability of rutin ethanolate at ambient conditions in contrast to the rutin trihydrate phase, which was found to be stable. Based on the particular solubility behavior of both solvate phases in ethanol a seeded crystallization process in batch and semi-continuous operation mode was designed and successfully performed. Crystalline rutin trihydrate of 99% purity was isolated with overall process yields of 95% and 87% in the batch and semi-continuous processes, respectively. Due to their cost-efficiency and robustness the purification processes are attractive to be applied directly in the countries, where the plants are gr...

Consolidated Bioprocessing for Butyric Acid Production from Rice Straw with Undefined Mixed Culture.

Lignocellulosic biomass is a renewable source with great potential for biofuels and bioproducts. However, the cost of cellulolytic enzymes limits the utilization of the low-cost bioresource. This study aimed to develop a consolidated bioprocessing without the need of supplementary cellulase for butyric acid production from lignocellulosic biomass. A stirred-tank reactor with a working volume of 21 L was constructed and operated in batch and semi-continuous fermentation modes with a cellulolytic butyrate-producing microbial community. The semi-continuous fermentation with intermittent discharging of the culture broth and replenishment with fresh medium achieved the highest butyric acid productivity of 2.69 g/(L· d). In semi-continuous operation mode, the butyric acid and total carboxylic acid concentrations of 16.2 and 28.9 g/L, respectively, were achieved. Over the 21-day fermentation period, their cumulative yields reached 1189 and 2048 g, respectively, corresponding to 41 and 74% of the maximum theoretical yields based on the amount of NaOH pretreated rice straw fed in. This study demonstrated that an undefined mixed culture-based consolidated bioprocessing for butyric acid production can completely eliminate the cost of supplementary cellulolytic enzymes.

Synthesis of isosorbide bis(methyl carbonate) by transesterification of isosorbide with dimethyl carbonate, and evidence of its usefulness as a monomer for manufacturing polycarbonates

Isosorbide bis(methyl carbonate) (IBMC) is a barely explored isosorbide derivative potentially useful as a monomer for synthesizing biobased polymers. In this paper, its synthesis by transesterification of isosorbide (IS) with dimethyl carbonate (DMC) at reflux temperature using potassium and cesium carbonates as catalysts is reported. Using a semicontinuous operation mode, a 97% yield was obtained with cesium carbonate as catalyst at a concentration of 0.2mol% vs. IS, and a DMC/IS molar ratio of 30. Oligomerization by reaction between IS, the intermediate isosorbide mono(methyl carbonate) and IBMC is a severe competitive reaction. Oligomers formation is strongly suppressed at high molar ratios and low catalyst concentrations. Cesium carbonate leads to a lower oligomer formation than potassium carbonate which is explained by the “cesium effect”. Evidence of the usefulness of IBMC as a biobased monomer for polymer synthesis through its polycondensation with 1,4-butanediol (1,4-BDO) is provided. A poly(isosorbide-1,4-BDO carbonate) with a weight average molar mass of 1800g/mol and a polydispersity of 1.43 is obtained in 63.4% yield using 3mol% DBU vs. IBMC as a catalyst with an IBMC/1,4-BDO molar ratio of 1 at 130°C.

The statistical optimization of bacterial cellulose production via semi-continuous operation mode

Bacterial cellulose (BC) is highly pure and has a higher crystallinity and molecular weight than plant cellulose. Therefore, BC can be used in many different areas such as biotechnology, pharmaceutical, cosmetics. Because of the price of BC, the productivity of BC is an important parameter for industrial scale applications. In this study, BC was produced in static culture using a semi-continuous operation mode; the conditions were optimized using response surface methodology (RSM). The collected BC was characterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and tensile strength. Optimization parameters were selected as glucose concentration, surface area/volume ratio, surface area and incubation day intervals. The optimum values for incubation day intervals, volume changing ratios, glucose concentrations and surface area/volume ratios were 7 days, 66%, 50g/L and 1.22cm−1, respectively. BC productivity reached 0.284g/L/day under optimal conditions, while the model equation proposed 0.289g/L/day. RSM is essential for determining the optimum values of parameters for BC production compared with the one-variable-at-a-time method. The semi-continuous operation mode is alternative and a good candidate for the industrial scale production of BC.

Enhancement of rice vinegar production by modified semi-continuous culture based on analysis of enzymatic kinetic

Product inhibition is the main problem of high-strength rice vinegar fermentation by Acetobacter pasteurianus. An optimized semi-continuous operation mode was proposed with a modified starting-up protocol which can improve the average acetification rate 35 % higher than original one. First, we revealed PQQ-ALDH is the rate-limiting enzyme responsible for ethanol oxidation route, whose apparent K m of PQQ-ADH and PQQ-ALDH is 1.89 and 7.80 mM, respectively. Further work elucidated that PQQ-ALDH follows ordered Bi–Bi mechanism which indicated that Co Q can improve the reaction. Among five Co Q precursors, supplementation of 20 mM isopentenyl alcohol got the best result, which improved strain acid resistance ability that accelerates biomass accumulation. A two-stage starting-up protocol was developed, which reduced the duration of the starting-up process from 45 to 34 h. An optimized semi-continuous operation mode was proposed whose whole operation time reduced from 116 to 98 h and average acetification rate has been raised to 1.77 g/Lh, while the original is 1.31 g/Lh. The average activity of ALDH is 43 % higher than original process, while ADH is 19 %, which shows a good correlation with acetification rate.

Erratum to: Optimization of organic load for co-digestion of tannery solid waste in semi-continuous mode of operation

Solid waste generation from tanning industry is inevitable and is a major concern from an environmental pollution point of view. Co-digestion of tannery solid wastes is an attractive environmental-friendly option which contributes to decreasing the greenhouse gas emissions according to the Kyoto protocol. In the present study, the reactors were operated in semi-continuous mode with volatile solids (VS) input of 38, 45, 53, 60, 68, and 145 g in 6 feeds to evaluate the effect of multiple feeds on co-digestion process. At the VS load of 68 g, biogas generation per gram of VSadded was 470 mL. At this VS load, maximum % of volatile fatty acids (VFAs) reduction was observed, and hence the VS load of 68 g was found to be optimum from the various VS loads investigated in the present study. The ratio of VFA/alkalinity was in the range of 0.206–0.714, and stable conditions prevailed during co-digestion of tannery wastes. This optimization of organic loading rate and performance evaluation data is useful for full-scale implementation of co-digestion process in the tannery sector for management of solid waste.

Optimization of organic load for co-digestion of tannery solid waste in semi-continuous mode of operation

Optimization of organic load for co-digestion of tannery solid waste in semi-continuous mode of operation

Improvement production of bacterial cellulose by semi-continuous process in molasses medium

Bacterial cellulose (BC) has unique properties such as structural, functional, physical and chemical. The mass production of BC for industrial application has recently become attractive to produce more economical and high productive cellulose. In this study, to improve the productivity of bacterial cellulose (BC), BC production by Gluconacetobacter xylinus FC01 was investigated in molasses medium with static semi-continuous operation mode. Cell dry weight, polysaccharide, sugar and cellulose concentrations were monitored and cellulose was characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The highest cellulose yield (1.637g/L) was obtained in SCP50-7d, which molasses of 1/2 ratio for 7 days by static semi-continuous operation mode. The results show that BC can be highly produced by G. xylinus in molasses with static semi-continuous process than batch process. We claimed that low-cost medium with semi-continuous operation mode in static culture is a good candidate for industrial scale BC productions.

Experimental studies on the effect of harvesting interval on yield of Scenedesmus arcuatus var. capitatus

Absorption of CO2 and light in desired quantity plays a key role in photosynthesis for CO2 sequestration by microalgae. The growth of microalgae undergoes lag, log, stationary and deceleration phases resulting in increased growth rate upto an optimum biomass concentration and then decreased beyond that concentration. Variation of rate with biomass concentration affects the overall performance. Maintenance of growth rate always at the maximum level will reduce the reactor size and hence the cost. Therefore, a process strategy required for maintaining maximum growth rate of microalgae is proposed in the present study. The proposed strategy is to harvest the microalgae at periodic intervals to maintain the optimum biomass concentration inside the reactor by semi-continuous mode of operation. The effect of the proposed strategy on the overall yield was examined by conducting the experiments on the growth of Scenedesmus arcuatus var. capitatus with a culture depth of 0.5cm by batch and semi-continuous modes. Comparing the yields, it is found that the proposed strategy increased the yield by 35% when harvested at a periodic interval of 5h, over the batch mode.

Industrial Waste Utilization for Low-Cost Production of Raw Material Oil Through Microbial Fermentation

In view of ever-growing demand of biodiesel, there is an urgent need to look for inexpensive and promising renewable raw material oils for its production. In this context, the aim of this study was to evaluate the potential use of industrial wastes for low-cost production of oils through microbial fermentation. Among the strains tested, Yarrowia lipolytica grew best and produced highest lipid when grown on decanter effluent from palm oil mill. When crude glycerol by-product from a biodiesel plant was added into the effluent as a co-substrate, Y. lipolytica produced a higher biomass of 3.21 g/L and a higher amount of lipid of 2.21 g/L which was 68 % of the dry weight. The scale up and process improvement in a 5-L bioreactor increased the biomass and lipid up to 5.53 and 2.81 g/L, respectively. A semi-continuous mode of operation was an effective mode for biomass enhancement while a fed-batch mode was effective for lipid enhancement. These yeast lipids have potential to be used as biodiesel feedstocks because of their similar fatty acid composition to that of plant oil.