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Abstract The preserved greengage is a favorite dried fruit in China. In processing preserved greengages, the drying of salted greengages is a key and energy-consuming process. Traditionally, the drying of salted greengages mainly relies on natural sun drying and requires about 48 days. In this study, an attempt was made using solar driers with fresh fruit that have been mixed with some salt and preserved in a concrete pool for more than 2 months. A solar drier, consisting of 6 m2 of solar air collectors, a greenhouse-like drying chamber and three fans powered by a solar module of 20Wp, was developed and examined, and a comparative experiment between solar drying and natural sun drying was conducted from 26 April to 12 June, 2003. The experiment found that, even in cloudy days, the temperature of the drying air inside the chamber was much higher than that of the ambient air, and solar drying of salted greengages was very effective. Thus the drying period was shortened from 48 days in natural sun drying to about 15 days. It was also found that the solar drying could eliminate a process that takes 20 days to desalt salted greengages to obtain the final product as required in the natural sun drying method.

Abstract Black soldier fly larvae with high contents of lipids can be used as a novel biomass feed-stock. An efficient approach involving surfactants assisted extraction of lipid from the wet biomass in this study. Surfactants with functional molecular structure were found to be helpful to extract lipids in the extraction process. Control experiments were performed to investigate the influence of different factors (surfactant types, surfactant concentration, salt concentration, and extraction temperature) on the lipid extraction process from the wet energy biomass. These results suggested that the extraction capacity of lipid was 78.99% at the defined condition (solvent:water = 50 mL:30 mL, biomass:solvent = 30 g:50 mL, surfactant concentration = 0.5%, extraction time = 60 s, extraction temperature = 60 °C). In addition, the purities of saponifiable lipids for these surfactants used were more than 80% in the present work. Surfactant treatment had a weak effect on lipids compositions. The kinetic model of the surfactants assisted lipid extraction process was proposed. During solvent extraction, the extraction process is divided to the two main processes: washing process and diffusion process. The rate constants were 4.17 × 10−2 to 5.94 × 10−2 in the first stage and 1.43 × 10−3 to 2.78 × 10−3 in the second stage for surfactants treatment, respectively. The second stage constitutes the limitation step in the extraction process. Further, the results of thermodynamic parameters were determined from thermodynamic study of lipid extraction process. This research showed the surfactant assisted route is a high efficiency technique.

Abstract Humic acid (HA) containing in the inoculated waste activated sludge (WAS) would be released into the fermentation liquid during dark fermentative hydrogen production. Nevertheless, the influence of HA on the photofermentative hydrogen production from volatile fatty acids (VFAs) left in the dark fermentation liquid by photosynthetic bacteria (PSB) had not been investigated. This study measured the effects of sludge humic acid (SHA) and AQS (anthraquinone-2-sulfonic acid, model humic acid) on the photofermentative hydrogen production from VFAs. Results showed that the photofermentative hydrogen production was reduced by 12.0% and 35.4% in synthetic wastewater with 100 mg/L of the added SHA or AQS, respectively. Mechanistic studies showed that high concentrations of SHA and AQS inhibited the activity of nitrogenase and development of PSB biomass, as well as damaging the cell membranes and causing significant death of PSB, leading ultimately to a significant decrease of photofermentative hydrogen production. Moreover, fluorescence spectra showed that SHA had a small molecular weight and a low degree of humification compared to that of AQS, which caused more negatively influence of AQS on photo hydrogen generation from VFAs. Finally, the feasibility of removing SHA from anaerobic dark fermentation liquid of wastewater to improve photofermentative hydrogen production was testified.

Abstract Thermophilic anaerobic digestion (AD) is an efficient treatment process for waste activated sludge with enhanced hydrolysis and digestion rates. However, the costs associated with maintaining high temperature for thermophilic digester should be minimized and the thermal stability of the reactor should be maximized for its practical use. This study tested an integrated system consisting of a solar pond and an AD reactor for digestion of waste activated sludge. The integrated system could be stably operated at 51.6 ± 1.5 °C in sunny days (and nights) and maintained digestion performance over at least three days with cloud and rain. On the contrary, the control reactor without solar pond experienced significant temperature fluctuation and poor digestion performance. After 29d, the integrated system thermophilic reactor removed 65.0 ± 4.2% of total chemical oxygen demands and produced 79% excess biogas. The concentrations of soluble chemical oxygen demand, protein and saccharides in digester with solar pond were higher than those in that without the pond. Also, the presence of solar pond enhanced hydrolysis and degradation of soluble microbial byproduct-like compounds with carboxylic groups and amide-2 groups in sludge.

Abstract Cost-effectively drying of sewage sludge is the prerequisite step for further disposal, such as landfilling, incineration and pyrolysis. A novel solar drying method was developed using a thin layer sandwich-like chamber. The drying rate was optimized by adjusting the operating variables such as the thickness of sludge bed, and solar radiation intensity. Lower height of sewage sludge bed facilitates the faster drying process in thin layer sandwich-like solar drying chamber. In this experiment, the most suitable thickness of sewage sludge layer was found to be 0.5 cm for quick drying (average drying rate 6.72 g/h) under the sunlight in sandwich-like dryer. The water content in sewage sludge was decreased from 79% to 5% in 11 h drying with thickness of 0.5 cm under the solar radiation intensity of 500 W/m2. It was observed that the solar radiation influenced the drying process significantly, the drying time was reduced from 18 h to 9 h, as the solar radiation was increased from 300 W/m2 to 700 W/m2, respectively. To identify the drying kinetics of raw sewage sludge inside the sandwich-like drying chamber, eight established drying kinetics models were tried and compared the suitability of the model based on the R2, sum of square error (SSE), chi-square value, and root mean square error. Among these models, Danish model was found applicable for sewage sludge drying in this newly designed thin layer sandwich-like dryer. Based on the results obtained for solar drying of sewage sludge in thin layer sandwich-like drying chamber, it could be proposed that thin layer solar dryer may be a good choice for fast drying of sewage sludge in a cost-effective way.

The effects of thermal pretreatment (90, 120, 140 and 160 °C) on the morphology (organic and inorganic nitrogen) and distribution properties (in solid phase, liquid phase and gas phase) of nitrogen in kitchen waste (KW) and on anaerobic digestion performance were investigated. The results show that thermal pretreatment could efficiently enhance the solubilisation of organic nitrogen compounds in KW, especially at high temperatures and long heating durations. Approximately 3.0–47.9% of organic nitrogen in KW decreases in total nitrogen content was obtained in the solid phase after thermal pretreatment. Higher biogas production and biodegradability of organics (in terms of the removal rate of soluble chemical oxygen demand, total organic nitrogen, and volatile solids) during subsequent anaerobic digestion were observed compared with the levels for untreated KW. An overall economic analysis indicates that the most profitable pretreatment process was achieved at 90 and 120 °C for treatment time of 30 and 15 min respectively, with a net potential profit (2–8 € ton−1 kW).

Abstract Membrane distillation seawater desalination technology has received widespread attention. However, this technology has problems such as high energy consumption and high initial temperature requirements. A membrane distillation seawater desalination system integrated with low-concentrating photovoltaic/thermal (LCPV/T-MD) modules was designed. With the help of concentrating photovoltaic panels and solar collectors, the working fluid required for membrane distillation is cascaded heating to obtain distilled fresh water. The integrated LCPV/T-MD mathematical model the hybrid experimental system were established, and the thermal, electrical performance, and water yield were analyzed. The results show that the greater Δ P , the lower of the salinity c, and the higher the inlet water temperature Tin, the greater the water yield. The LCPV/T-STC heating subsystem can heat the water temperature above 60 °C, and then auxiliary heating by heating rod can meet the requirements of MD system for inlet water temperature. In the experiment, the thermal efficiency and the electrical efficiency of the system can reach 56.2% and 15.9%, respectively. The GOR of the total LCPV/T-MD system can reach 0.69, and the MD subsystem water yield can reach 0.579 L/(h·m2). The findings can provide guidance for the further study of membrane distillation.

Abstract This study compared a conventional granular anaerobic membrane bioreactor (CG-AnMBR) with a sponge assisted-granular anaerobic membrane bioreactor (SG-AnMBR) in terms of treatment performance, granular sludge properties, membrane fouling behaviour and biogas production. The SG-AnMBR showed better organics and nutrient removal, and enhanced methane yield at 156.3 ± 5.8 mL CH4 (STP)/g CODremoved. Granular sludge from the SG-AnMBR had superior quality with better settleability, larger particle size, higher EPS content and more granule abundance. The SG-AnMBR also exhibited slower fouling development with 50.7% lower total filtration resistance than those of the CG-AnMBR. Sponge addition effectively affected the concentration and properties of microbial products (e.g. soluble microbial products (SMP) and extracellular polymeric substances (EPS)) in granular sludge, cake layer as well as settling zone mixed liquor, thus alleviating the fouling propensity. The liquid chromatography-organic carbon detection (LC-OCD) analysis suggested that sponge addition reduced the concentrations of biopolymers, low molecular weight neutrals and acids, and building blocks of the foulants. Compared with the SG-AnMBR, GC-MS analysis confirmed the accumulation of volatile fatty acids, particularly acetic acid in the CG-AnMBR. It is evident that the SG-AnMBR could be a promising solution for improving overall G-AnMBR performance and substantially mitigating membrane fouling.

Abstract Wastewater sludge drying and incineration are conventional solids handling processes that are sometimes employed in water resource reclamation facilities. However, these two processes generate byproducts, sludge drying chaff and sludge incinerator ash, which are landfilled without taking advantage of their value. To gain value from these byproducts, a new synergistic catalytic pyrolysis process using chaff and ash was investigated in this study to improve energy production (i.e. generating a high yield pyrolysis gas) and generate useful products. Ash was used as a catalyst to decrease bio-oil that is corrosive and challenging for combustion in standard equipment, while increasing pyrolysis gas yield and energy for easier energy recovery. Ash increased the pyrolysis gas yield by 50% and product energy by nearly two-fold at the highest ash loading. The bio-oil volume was greatly reduced and contained fewer constituents based on GC-MS and GC-FID analyses. The product energy shifted from bio-oil to pyrolysis gas, which is relatively clean and easier for onsite energy recovery. Ca and Fe content in ash likely plays the catalytic role.