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This paper describes anaerobic thermophilic sludge digestion (55 °C) in a continuously stirred tank reactor (CSTR) on a pilot-plant scale (150 L). The experimental protocol was defined to examine the effect of the increase in the organic loading rate on the efficiency of the digester and to report on its steady-state performance. The reactor was subjected to a programme of steady-state operation over a range of solids retention times (SRTs) of 75, 40, 27, 20 and 15 days and organic loading rates (OLR) in the range 0.4–2.2 kg VS/(m3 day). The digester was fed with raw sludge (containing approximately 35 kg/m3 volatile solids (VS)) once daily during the 75-day SRT period, twice daily during the 40-day SRT period and three times a day during the 27-, 20- and 15-day SRT periods. The reactor was initially operated with an organic loading rate of 0.4 kg VS/(m3 day) and an SRT of 75 days. The volatile solids removal efficiency in the reactor was found to be 73%, while the volumetric methane production rate produced in the digester reached 0.02 m3/(m3 day). Over a 338-day operating period, an OLR of 2.2 kg VS/(m3 day) was achieved with 49.1% VS removal efficiency in the pilot sludge digester, at which time the volumetric methane production rate content of biogas produced in the digester reached 0.4 m3/(m3 day). The chemical oxygen demand (COD) mass balance obtained indicated that COD used for methane generation increased when the SRT was decreased or when the influent organic loading rate was increased. This implies that the amount of COD used in the anabolism route decreased with SRT due the microbial population becoming adapted to new operational conditions and more COD being used to generate methane.

Abstract Algae have been considered as a promising biodiesel feedstock. One of the major factors affecting large-scale algae technology application is poor wintering cultivation performance. In this study, an integrated approach is investigated combining freshwater microalgae Chlorella zofingiensis wintering cultivation in pilot-scale photobioreactors with artificial wastewater treatment. Mixotrophic culture with the addition of acetic acid (pH-regulation group) and autotrophic culture (control group) were designed, and the characteristics of algal growth, lipid and biodiesel production, and nitrogen and phosphate removal were examined. The results showed that, by using acetic acid three times per day to regulate pH at between 6.8 and 7.2, the total nitrogen (TN) and total phosphate (TP) removal could be increased from 45.2% to 73.5% and from 92.2% to 100%, respectively. Higher biomass productivity of 66.94 mg L−1 day−1 with specific growth rate of 0.260 day−1 was achieved in the pH-regulation group. The lipid content was much higher when using acetic acid to regulate pH, and the relative lipid productivity reached 37.48 mg L−1 day−1. The biodiesel yield in the pH-regulated group was 19.44% of dry weight, with 16–18 carbons as the most abundant composition for fatty acid methyl esters. The findings of the study prove that pH adjustment using acetic acid is efficient in cultivating C. zofingiensis in wastewater in winter for biodiesel production and nutrient reduction.

AbstractAgricultural organic wastes (AOW) have the potential to provide bioenergy particularly found in biogas by anaerobic digestion (AD). In this study, the biogas production (BP) of AOW was obtained by batch AD with anaerobic digesters (500 mL) at 35°C incubator. The results showed that BP values in terms of volatile solids (VS) from rice husk, rice straw, flower residues, fruit and vegetable residues, wasted oyster shell residue (WOSR), fishery residues, livestock and poultry manures, livestock and poultry slaughter wastes (LPSW), and eight equally mixed wastes (EEMW) were 84.03, 193.36, 153.32, 76.27, 150.48, 63.26, 169.63, 615.74, and 172.83 mL/g VS, respectively. LPSW showed the highest μm of 16.99 mL/g VS‐d, the highest BP of 615.74 mL/g VS and the highest bioconversion efficiency of 65.98% compared to the other organic wastes. BP from the most AOW in Taiwan by AD was estimated to be 768,567,753 (743,522,223, excluding WOSR) m3/year. The annual BP of 768,567,753 m3/year of the eight total major AOW by AD was lower (∼20.11%) than 961,989,781 m3/year of the EEMW by anaerobic co‐digestion. Result also showed that modified Gompertz equation was suitable to describe BP accumulation and BP rate.

AbstractIn this study, a novel solar tower-based gas turbine-driven multi-generation plant is proposed and analyzed in detail with energy, exergy, economic, and environmental impact analysis. A multiobjective optimization is performed by incorporating all performance indicators simultaneously. The proposed plant consists of an intercooling-regenerative-reheat solarized gas turbine cycle as the primary power cycle of a multi-generation plant for the first time. Two organic Rankine cycles are used to utilize waste heat of intercooling section and exhaust of gas turbine. To produce the multi-generation products of power, cooling, industrial process heating, fresh water, floor heating, green hydrogen, domestic hot water, hot air for food drying, and greenhouse heating, power cycles are integrated with a multi-effect desalination, a double-effect absorption refrigeration cycle, an electrolyzer, a drying hot air unit, a greenhouse heater, and an industrial process heater. A rigorous parametric analysis is performed to reveal the effects of variations of decision variables on the plant performance. At the optimum conditions, energy efficiency, exergy efficiency, average unit product exergy cost, and emission savings values are determined as 57.23%, 40.7%, 0.08315 $/kWh, and 948.7 kg CO2/h, respectively. Moreover, proposed plant can produce 1962 kW power and 3.353 kg/h hydrogen in addition to other utilities with a system cost rate of 0.05134 $/s and 3226 kW exergy destruction rate.

Rivers are important sources of freshwater and nutrients for the Mediterranean and Black Sea. We present a reconstruction of the spatial and temporal variability of these inputs since the early 1960s, based on a review of available data on water discharge, nutrient concentrations and climatic parameters. Our compilation indicates that Mediterranean rivers suffer from a significant reduction in freshwater discharge, contrary to rivers of the Black Sea, which do not have clear discharge trends. We estimate this reduction to be at least about 20% between 1960 and 2000. It mainly reflects recent climate change, and dam construction may have reduced discharge even further. A similar decrease can also be expected for the fluxes of dissolved silica (Si), strongly controlled by water discharge and potentially reduced by river damming as well. This contrasts with the fluxes of nitrogen (N) and phosphorus (P) in Mediterranean and Black Sea rivers, which were strongly enhanced by anthropogenic sources. Their total inputs to the Mediterranean Sea could have increased by a factor of >5. While N still remained at elevated levels in 2000, P only increased up to the 1980–1990s, and then rapidly dropped down to about the initial values of the 1960s. With respect to the marine primary production that can be supported by the riverine nutrient inputs, Mediterranean and the Black Sea rivers were mostly phosphorus limited during the study period. Their anthropogenic nutrient enrichment could only have had a fertilizing effect before the general decline of the P loads. When also considering Si as a limiting element, which is the case for siliceous primary producers such as diatoms, silica limitation may have become a widespread phenomenon in the Mediterranean rivers since the early 1980s. For the Black Sea rivers, this already started the late 1960s. Gross primary production sustained by rivers (PPR) represents only less than 2% of the gross production (PP) in the Mediterranean, and less than 5% in the Black Sea. Possible ecological impacts of the changing river inputs should therefore be visible only in productive coastal areas, such as the Gulf of Lions, where PPR can reach more than two thirds of PP. Reported ecosystem changes both in the Adriatic Sea and the Black Sea are concomitant with major changes in the reconstructed river inputs. Further work combining modelling and data collection is needed to test whether this may also have been the case for coastal ecosystems at other places in the Mediterranean and Black Sea.

Abstract A coiled-pipe exchanger was employed to extract heat rapidly at relatively high temperatures from a 90-litre hot-water charged tank, the water being initially at a temperature of approximately 80°C. The free-convective movements of the water around the outside of the coiled pipe (immersed in the store) were due to buoyancy forces induced by colder water being forced through the heat-exchanger's pipe. For the heat-exchanger orientations tested, the maximum effectiveness, with respect to the quality of the heat extracted was achieved (i) by having the axis of the coiled heat-exchanger arranged horizontally with its inlet at the lowest level; and (ii) with the lower rate tested (=6·6 litre/min) of water being passed through the heat-exchanger's pipe, partly because this led to a lower rate of disruption of the stratification of the water within the store.

Abstract The freeze-melting process can be a viable method for the purposes of desalination because of its low energy consumption, ignorable corrosion issues, and without huge pressure or membrane replacement work. Large contact area for heat and mass transfer per unit mass of water between the water and air and low heat resistance results in higher energy efficiency during spray freezing desalination process compared to other freezing desalination methods. A 200 m high desalination tower was proposed in this paper that could generate 27.7 kg/s fresh water in the form of water droplets with 2 mm diameter at an atmospheric temperature of −26°C. This research has founded that the natural convective airflow induced by the heat released by the warm water in the freezing process could generate through the wind turbine mounted in this system approximately one-third of the energy consumed by the water pump of the system. This free energy has never been studied in previous research. The power consumption required to produce 1 m3 fresh water in this system is approximately 1.07 kWh. Compared to traditional desalination methods, the power consumption of our new spray freezing desalination system is much lower than previous systems with the same mass flow rate of fresh water. Only 375.4 kJ cold energy to produce one-kilogram fresh water. Thus, this spray freezing desalination system could be employed in desalination industry if free cold energy (e.g. from the cold atmosphere or the regasification process of LNG) and seawater resources are available.

Psychrophilic anaerobic treatment is an attractive option for wastewaters that are discharged at moderate to low temperature. The expanded granular sludge bed (EGSB) reactor has been shown to be a feasible system for anaerobic treatment of mainly soluble and pre-acidified wastewater at temperatures of 5--10 degrees C. An organic loading rate (OLR) of 10--12 kg chemical oxygen demand (COD) per cubic meter reactor per day can be achieved at 10--12 degrees C with a removal efficiency of 90%. Further improvement might be obtained by a two-module system in series. Stabile methanogenesis was observed at temperatures as low as 4--5 degrees C. The specific activity of the mesophilic granular sludge was improved under psychrophilic conditions, which indicates that there was growth and enrichment of methanogens and acetogens in the anaerobic system. Anaerobic sewage treatment is a real challenge in moderate climates because sewage belongs to the 'complex' wastewater category and contains a high fraction of particulate COD. A two-step system consisting of either an anaerobic up-flow sludge bed (UASB) reactor combined with an EGSB reactor or an anaerobic filter (AF) combined with an anaerobic hybrid reactor (AH) is successful for anaerobic treatment of sewage at 13 degrees C with a total COD removal efficiency of 50% and 70%, respectively.