Employing response surface methodology (RSM) to improve methane production from cotton stalk

Biosynthesis of (S)-1-(1-naphthyl) ethanol by microbial ketoreductase

(S)-1-(1-naphthyl) ethanol (SNE) is a chiral drug intermediate for the production of mevinic acid analog, a potent cholesterol agent. It acts as an HMG-CoA reductase inhibitor and is hence used in the synthesis of statins. Statins are lipid-lowering drugs used to lower cholesterol in the body. In our present study, we carried out whole-cell bioreduction of 1-Acetonaphthone to enantiopure SNE using selected microorganisms acquired by soil acclimation technique. The microorganism which exhibited higher bioreduction activity was determined using high-performance liquid chromatography (HPLC), and it was identified as Pichia kudriavzevii by ITS primer sequencing. After optimizing the parameters, Pichia sp. produced SNE with good conversion (75%), yield (67%), and excellent enantiomeric excess (100%). The microbial enzyme showed higher activity at 24-h-old supernatant. The crude and partially purified enzyme exhibited a specific activity of 51.13 U/mL and 62.72 U/mL, respectively, with a 1.22 purification fold.

Influences of organic loading, feed-to-inoculum ratio, and different pretreatment strategies on the methane production performance of eggplant stalk

A large amount of eggplant stalk (ES) is incinerated after harvesting of eggplant every year, which aggravates environmental pollution and waste of resources. Converting ES into methane through anaerobic digestion (AD) technology may be a potential treatment method, considering the low environmental impact and high energy recovery. Firstly, this study explored the effects of organic loading (OL) and feed to inoculum ratio (F/I ratio) on the AD of ES by response surface methodology (RSM). In order to achieve higher AD efficiency, various pretreatments (acid, alkali, alkaline hydrogen peroxide (AHP), microwave, and ultrasound) were introduced and comprehensively assessed with regard to methane production, organic matter destruction, and kinetic parameters. Results showed that OL had a more significant impact on AD process compared to F/I ratio and methane production was enhanced remarkably when the OL and F/I ratio were 35.0 g VS/L and 3.0, respectively. XRD, FTIR, and SEM analyses of pretreated ES showed that alkali and AHP pretreatments performed better in delignification. Under optimal conditions, the ES pretreated with 1.5% AHP (adjusted by KOH) performed the maximum methane production of 262.2 mL/g VS with a biodegradability of 95.0%, which increased by 334.1% compared to untreated ES. This paper not only provides the theoretical data about methane production performance of ES but also gives practical guidance for efficient utilization of similar vegetable stalk biowastes, which is also promising for large-scale industrial applications in the future.

Optimization-Based Water-Salt Dynamic Threshold Analysis of Cotton Root Zone in Arid Areas

Threshold levels of soil moisture and salinity in the plant root zone can guide crop planting and farming practices by providing a baseline for adjusting irrigation and modifying soil salinity. This study describes a method of soil water and salinity control based on an optimized model for growing cotton in an arid area. Experiments were conducted in Akesu Irrigation District, southern Xinjiang, northwest China, to provide data for cotton yield and soil water content and salinity in the root zone at different growth stages. The sensitivity of cotton to soil water content and salinity was predicted for different growth periods using a modified Jensen model. An optimization model with 480 boundary conditions was created, with the objective of maximizing yield, to obtain the dynamically varying water and salt threshold levels in the root zone for scenarios that included three initial soil moisture content values (W0), eight irrigation quantities (M), five initial soil salt content values (S0), and four irrigation water salinity levels (K). Results showed that the flowering–boll stage is the crucial period for cotton yield, and the threshold levels of soil water content and salinity in the cotton root zone varied with the boundary conditions. The scenario chosen for the research area in this study was W0 = 0.85θfc (θfc is field capacity), S0 = 4 g kg−1, M = 400 mm, K = 0 g L−1. The predicted threshold levels of soil water for different growth stages (seedling, bud, flowering–boll, and boll-opening) were respectively 0.75–0.85θfc, 0.65–0.75θfc, 0.56–0.65θfc, and 0.45–0.56θfc. Corresponding threshold levels of salt were 4–4.16, 4.16–4.39, 4.39–4.64, and 4.64–4.97 g kg−1 when no action was taken to remove salt from the root zone. This study provides an innovation method for the determination of dynamically varying soil water content and salt thresholds.

Study of biological and thermo-chemical pretreatment of organic fraction of municipal solid waste for enhanced biogas yield

Biogas production from organic fraction of municipal solid waste (OFMSW) not only helps in solid waste management but also combat the food vs fuel dilemma. The presence of lignocellulosic material and other complex compounds in OFMSW hinder biogas production. Therefore, pretreatment is an essential step to increase the hydrolysis rate by converting complex compounds to simpler ones. This work was aimed at effective pretreatment of OFMSW by biological and thermo-chemical means. For biological pretreatment lignin degrading fungal strains, Phanerochaete chrysosporium and Pleurotus ostreatus were employed. Thermo-chemical treatment resulted in higher solubilisation yield in terms of sCOD and VFA making it a more effective method as compared with biological pretreatment. The optimisation of thermo-chemical pretreatment was done by the Box-Behnken design of response surface methodology (RSM). The interactive effect of influencing factors NaOH dose, temperature and time were studied on the response of sCOD, VFA and phenolic content. The sCOD and VFA values were significantly increased by increasing the NaOH concentration, temperature and time to a certain limit. The optimised condition from RSM for maximum solubilisation yield in terms of sCOD, VFA and phenolic content was found to be NaOH dose of 4.72 g/L, temperature 180 °C and time 30.3 min. Biogas production was increased by 169.5% after pretreatment at RSM optimised conditions as compared with untreated OFMSW.

Assessment of wastes recycling for deinking purposes in ozone assisted green process

This study investigates techno-economic aspects of wastepaper recycling to optimize process efficiency and operating cost. The deinking was carried out using pulping followed by froth flotation. The development of a waste management process was achieved employing refinery wastewater to provide chemical reagents in pulping. Ozone was also used as a gas media in flotation to improve brightness and number of ink-spot and to reduce chemical oxygen demand (COD) simultaneously. An enhancement in the brightness was observed from 50.1 to 64.1% ISO that was superior to the brightness of virgin newspaper before printing (61.0% ISO). It was equivalent to a reduction of 55% (from > 100,000 to 45,058) in number of ink-spot. The quality of flotation effluent was assessed by measuring the COD and phthalocyanine concentration. The COD reduction of 67% (from 3250 to 1072 mg/L) and phthalocyanine reduction of 85% (from 2 to 0.3 mg/L) were achieved after 30 min ozonation. According to the obtained results, approximately 67% of the direct (variable) cost reduced while the wastewater was used in pulping because of saving NaOH and water consumption. Associating the refinery and paper recycling wastewater treatment units, while taking into account the environmental and economic benefits of ozone, results in a quality paper and significantly preserves the environment.

Effect of organic loading, feed-to-inoculum ratio, and pretreatment on the anaerobic digestion of tobacco stalks

This work firstly investigated the suitable organic loading (OL) and feed to inoculum (F/I) ratio of three kinds of tobacco stalks (TS116, TS99, and TS85) during anaerobic digestion (AD) via response surface methodology (RSM). The highest experimental methane yield (EMY) of 148.1 mL/g VS was achieved from TS116 at OL of 20.2 g VS/L and F/I ratio of 1.1. To further increase EMY, various pretreatments including alkaline hydrogen peroxide (AHP), NaOH, KOH, Ca(OH)2, HCl, and oxalic acid (H2C2O4) were implemented on TS116. Results showed that AHP was most effective, and the maximal EMY of 350.7 mL/g VS and biodegradability (Bd) of 81.4% were obtained from 7% AHP pretreated TS116, which increased by 105.6% than untreated. XRD, FTIR, and SEM analyses evidenced that the structure of AHP pretreated TS116 was strongly disrupted. This study lays the foundation for applying this waste into AD in future applications.

Optimizing key factors for biomethane production from KOH-pretreated switchgrass by response surface methodology

Anaerobic digestion (AD) is one of the best technologies for producing methane from biomass wastes with limited environmental impacts. Most AD plants need a continuous and stable supply of feedstock for their sustained operation for which lignocellulosic biomass can be effectively utilized. Switchgrass (SG), also known as Panicum virgatum, is a tall-growing grass which exists throughout the year in areas with warm climate and has the potential to produce biomethane. The present work investigated anaerobic digestion performance of SG while focusing on enhancing the methane yield by employing central composite design of response surface methodology (RSM). The aim of this research was to find out the best level of factors including feed-to-inoculum (F/I) ratio, organic loading (OL), and pH for optimizing the desired output of biomethane production from 3% KOH-pretreated SG. Results revealed that the highest value of experimental methane yield was 288.4 mL/gVS at the optimal F/I ratio, pH, and OL of 1, 6.96, and 24 gVS/L, respectively. Moreover, 3% KOH pretreatment improved the biodegradability of SG significantly from 14.23 to 85.53%. This study forms the basis for future application of SG for enhanced methane production.

Anaerobic digestion of tobacco stalk: biomethane production performance and kinetic analysis

Tobacco stalk, a common agricultural waste derived from the harvest of tobacco, caused serious environmental pollution in China. In this study, the performance of biomethane production and characteristics of four varieties of tobacco stalk were investigated for the first time. The results showed that the highest cumulative methane yield of 130.2 mL/g-VS was obtained from Nicotiana tabacum L., Yunyan114, which had lower lignin content than other varieties of tobacco stalk. Moreover, different kinetic models were used to describe the biomethane production process, and it was found that the modified Gompertz model was more suitable to simulate the anaerobic digestion (AD) of tobacco stalk. The findings of this study not only showed a feasible method for minimizing the pollution issues of tobacco stalk waste but also gave fundamental information for future AD application.