New wastewater treatment concepts towards energy saving and resource recovery

At present, conventional activated sludge (CAS) systems are widely applied to treat municipal wastewater. The main advantages of CAS systems are that they are robust and generally produce an effluent quality that meets the discharge guidelines. However, CAS systems cannot be considered sustainable because they consume large amounts of energy (mainly for aeration and sludge treatment), have a high CO2 emission and do no recover a potential resource of water, energy and nutrients nitrogen (N) and phosphorus (P). Therefore, in this thesis new municipal wastewater treatment concepts that combine treatment with recovery of valuable resources and can save considerable amounts of energy were investigated by modelling and experiments.Quantitative numerical results showed that the feasibility of two novel wastewater treatment configurations, including combined bioflocculation and anaerobic digestion but with different nutrient removal technologies, i.e. (cold) partial nitritation/Anammox or microalgae treatment, is location dependent. Using Dutch municipal wastewater and climate conditions, the configuration with cold partial nitritation/Anammox is the most promising wastewater treatment concept, because it can: 1) treat wastewater year round; 2) produce an effluent at a quality that meets the discharge guidelines; 3) reduce CO2 emission by 35% compared to the CAS system; 4) achieve a net energy yield up to 0.24 kWh per m3 of wastewater compared to a negative net energy yield of -0.08 kWh per m3 of wastewater for the CAS system; and 5) recover 80% of the sewage P. Additionally, the feasibility of the two configurations was investigated for 16 locations around the globe. The results quantitatively support the pre-assumption that the configuration with (cold) partial nitritation/Anammox is applicable in tropical regions and some locations in temperate regions. The configuration with microalgae treatment is only applicable the whole year round in tropical regions that are close to the equator line. The results also showed that the configuration employing microalgae treatment has an advantage over the configuration employing partial nitritation/Anammox with respect to consumption of aeration energy and recovery of nutrients, but not with respect to area requirements. For a tropical climate country like Thailand, the net energy yield of both configurations is at least a factor 10 higher than the CAS system, while CO2 emission is at least 22% lower.In CAS systems energy recovery from wastewater is accomplished by anaerobic digestion of the organic solids in primary and secondary sludge into methane. However, volatile fatty acids (VFA), which are intermediate digestion products, may be preferred over methane, because VFA can be used as starting compounds for a wide range of higher value products. In this thesis the experimental results showed that a combined process with bioflocculation, using a high-loaded membrane bioreactor (HL-MBR) to concentrate sewage organic matter, and anaerobic fermentation, using a sequencing batch reactor to produce VFA is technologically feasible. An HL-MBR operated at a hydraulic retention time (HRT) of 1 hour and a sludge retention time (SRT) of 1 day resulted in very good performance, because as high as 75.5% of the sewage COD (chemical oxygen demand) was diverted to the concentrate and only 7.5% was mineralized into CO2. It was also found that 90% of the sewage NH4-N and PO4-P were conserved in the HL-MBR permeate, which can be reused as irrigation water as it is free from solids and pathogens.During anaerobic fermentation of the HL-MBR concentrate at an SRT of 5 days, 35°C and without pH control, methane production was inhibited, but incomplete solids degradation mainly limited the VFA production as only 15% of the sewage COD was converted to VFA. Thus, the VFA yield needed to be increased. It was hypothesized that high pH (pH 8–10) fermentation combined with a long SRT, allowing for sufficient solubilization of solids and colloidal COD, can improve the VFA yield. In the current study, it was found that application of a pH shock of 9 in the first 3.5 hours of a sequencing batch cycle followed by a pH uncontrolled phase for 7 days gave the highest VFA yield of 440 mg VFA-COD/g VSS and this was equivalent to 26% of the sewage COD. This yield was much higher than at fermentation without pH control or at a constant pH between 8 and 10. The high yield in the pH 9 shock fermentation could be explained by: 1) a reduction of methanogenic activity; or 2) a high degree of solids degradation; or 3) an enhanced protein hydrolysis and fermentation. This study also demonstrated that the VFA yield can still be further optimized by fine-tuning pH levels and longer operation, possibly with fermentative microorganisms adapted to a high pH that are commonly found in nature. This would further increase VFA yield to 33% of the sewage COD.<br/

Energy reduction for commercial freezer by force convection cooling of heatsink

Commercial freezers are commonly used the outer wall as a heatsink. This heatsink needs surrounded ambient air for cooling, which is the natural convection mechanism. However, in theory the force convection provides more heat transfer than the natural convection. Therefore, energy consumption of the force convection is generally less than the natural convection. This study aims at testing and comparing the heat transfer between the natural convection and force convection of the heatsink of the commercial freezer. Moreover, this study investigated the potential of energy reduction of the freezer by using the natural convection and the force convection of the heatsink. In this study, the unmodified commercial freezer installed with the wind tunnel over the heatsink of the freezer was made. The necessary parameters such as heatsink surface temperature, cooling air temperature, ambient air temperature, velocity of cooling air, and power consumption of the freezer were collected. The testing conditions were varied the internal heat load of the freezer by using water as 0, 3, and 6 kg, and varied the cooling air velocity as 0, 1, 2, and 3 m/s. The results showed that the convection mechanism was significantly affected by energy consumption. Furthermore, it was clearly found that the heat transfer for the force convection was higher than the natural convection. Moreover, the use of force convection resulted in a lower energy consumption. In particular at the internal heat load of 6 kg, the energy consumption of the force convection decreased by 17.5%, 17.7%, and 20.5% as compared to the natural convection at the cooling air velocity of 1, 2, and 3 m/s, respectively. Based on the results obtained it can be concluded that the force convection for the freezer heatsink can be used to reduce energy consumption, which could be efficiently applied in the future works

The Dietary effects on manure characteristics and biogas production from dairy cows feeding with pineapple peel

RMUTP Research Journal, Vol. 16, No. 1, January-June 2022, pp.1-12This study explored the dietary effect on manure characteristics and potential of biogas production from the manure of dairy cows feeding with pineapple peel as a roughage source. Three mid-lactation primiparous crossbred Holstein dairy cows, which had an average body weight of 443.5±10.6 kg and average milk production of 9.6±0.3 kg/d were assigned with three different diet types including T1, T2 and T3. T1 was a control diet, which consisted of a mixture of dry Pangola grass and commercial pellet (CL). Moreover, T2 was a mixture of dry Pangola grass, pineapple peel and CL, while T3 was a mixture of pineapple peel and CL. Dairy cow manure was collected on the day 10th after feeding and anaerobic digestion of the dairy cow manure was operated with an HRT of 30 days. Results showed that all diet types gave similar manure characteristics of high organic matter and nitrogen. Average concentrations of TS and COD ranged from 82.59 to 85.78 g/L and 85.47 to 91.47 g/L, respectively, whereas TAN ranged from 1.54 to 1.67 g/L. However, a higher pH of 7.50 was found for the manure of dairy cow fed with T1, while a lower pH of 6.50 was obtained with T3. Besides, the highest methane yield of 0.20 m3 CH4/kg VSadded was obtained when using the manure of dairy cow fed with T1 as a substrate, followed by T2 and T3 which found at 0.14 and 0.11 m3 CH4/kg VSadded, respectively. This indicated the efficient potential of biogas production from the manure of dairy cows fed with pineapple peel, which will improve sustainable utilization of agricultural wastes and waste produced from dairy cow farm in the future.Rajamangala University of Technology Phra Nakho

Glocal assessment of integrated wastewater treatment and recovery concepts using partial nitritation/Anammox and microalgae for environmental impacts

This study explored the feasibility and estimated the environmental impacts of two novel wastewater treatment configurations. Both include combined bioflocculation and anaerobic digestion but apply different nutrient removal technologies, i.e. partial nitritation/Anammox or microalgae treatment. The feasibility of such configurations was investigated for 16 locations worldwide with respect to environmental impacts, such as net energy yield, nutrient recovery and effluent quality, CO2 emission, and area requirements. The results quantitatively support the applicability of partial nitritation/Anammox in tropical regions and some locations in temperate regions, whereas microalgae treatment is only applicable the whole year round in tropical regions that are close to the equator line. Microalgae treatment has an advantage over the configuration with partial nitritation/Anammox with respect to aeration energy and nutrient recovery, but not with area requirements. Differential sensitivity analysis points out the dominant influence of microalgal biomass yield and wastewater nutrient concentrations on area requirements and effluent quality. This study provides initial selection criteria for worldwide feasibility and corresponding environmental impacts of these novel municipal wastewater treatment plant configurations

Production of volatile fatty acids from sewage organic matter by combined bioflocculation and alkaline fermentation

This study explored the potential of volatile fatty acids (VFA) production from sewage by a combined high-loaded membrane bioreactor and sequencing batch fermenter. VFA production was optimized with respect to SRT and alkaline pH (pH 8–10). Application of pH shock to a value of 9 at the start of a sequencing batch cycle, followed by a pH uncontrolled phase for 7 days, gave the highest VFA yield of 440 mg VFA-COD/g VSS. This yield was much higher than at fermentation without pH control or at a constant pH between 8 and 10. The high yield in the pH 9 shocked system could be explained by (1) a reduction of methanogenic activity, or (2) a high degree of solids degradation or (3) an enhanced protein hydrolysis and fermentation. VFA production can be further optimized by fine-tuning pH level and longer operation, possibly allowing enrichment of alkalophilic and alkali-tolerant fermenting microorganisms

Energy and nutrient recovery for municipal wastewater treatment: How to design a feasible plant layout?

Activated sludge systems are commonly used for robust and efficient treatment of municipal wastewater. However, these systems cannot achieve their maximum potential to recover valuable resources from wastewater. This study demonstrates a procedure to design a feasible novel configuration for maximizing energy and nutrient recovery. A simulation model was developed based on literature data and recent experimental research using steady-state energy and mass balances with conversions. The analysis showed that in the Netherlands, proposed configuration consists of four technologies: bioflocculation, cold partial nitritation/Anammox, P recovery, and anaerobic digestion. Results indicate the possibility to increase net energy yield up to 0.24 kWh/m3 of wastewater, while reducing carbon emissions by 35%. Moreover, sensitivity analysis points out the dominant influence of wastewater organic matter on energy production and consumption. This study provides a good starting point for the design of promising layouts that will improve sustainability of municipal wastewater management in the future

Investigation of the physical properties and environmental impact of lemongrass biobriquettes

At present, biobriquettes have become an attractive fuel option due to the increasing price of fossil fuels. However, the effective raw materials for biobriquettes require specific physical properties to obtain desired shapes and net calorific value. Therefore, the objective of this study was to explore a raw material with appropriate physical properties for biobriquettes. In this study, lemongrass was used as raw material for biobriquettes which formed by mixing with charcoal and a binder. The basic physical properties of biobriquettes, such as density, moisture content, net calorific value, ash content, volatile matter, and carbon content, were analyzed. Moreover, the net calorific value and the carbon content were determined to find the carbon dioxide (CO2) emission factor. The amount of CO2 emission when using lemongrass biobriquettes substituted for the conventional biomass sources was also determined. The results showed that the density varied depending on the pressure compaction conditions. Besides, the carbon content was successfully determined and reported. The average net calorific value under all compression pressures was reported. The net calorific value of lemongrass biobriquettes was higher than that of firewood and most agricultural wastes, with an average CO2 emission factor of 77,362 kgcarbon/TJ. Based on all the results obtained, it can be concluded that lemongrass biobriquettes produce a lower CO2 emission than firewood, most agricultural wastes, and charcoal; therefore, it is suitable as an alternative biofuel in the future

Exploring the feasibility of a novel municipal wastewater treatment system via dynamic plant-wide simulation

A plant-wide simulation study is presented in which we investigated the feasibility of a novel centralized municipal wastewater treatment system design as previously proposed by Khiewwijit et al. (2015). This design includes processes as bioflocculation (BF), anaerobic digestion (AD), partial nitritation (PN) and Anammox (ANA). We specifically investigate the effects of operational conditions (SRT, HRT, dissolved oxygen set point and temperature) on carbon recovery potential and ability to meet N discharge criteria according to European legislation. The results suggest that BF-AD can be a promising technology combination for carbon recovery. However, PN-ANA is as yet not suitable for European conditions within the context of studied design at the current state of technology development.</p

Production of volatile fatty acids from sewage organic matter by combined bioflocculation and alkaline fermentation

This study explored the potential of volatile fatty acids (VFA) production from sewage by a combined high-loaded membrane bioreactor and sequencing batch fermenter. VFA production was optimized with respect to SRT and alkaline pH (pH 8–10). Application of pH shock to a value of 9 at the start of a sequencing batch cycle, followed by a pH uncontrolled phase for 7 days, gave the highest VFA yield of 440 mg VFA-COD/g VSS. This yield was much higher than at fermentation without pH control or at a constant pH between 8 and 10. The high yield in the pH 9 shocked system could be explained by (1) a reduction of methanogenic activity, or (2) a high degree of solids degradation or (3) an enhanced protein hydrolysis and fermentation. VFA production can be further optimized by fine-tuning pH level and longer operation, possibly allowing enrichment of alkalophilic and alkali-tolerant fermenting microorganisms