Static supply of different simulated flue gases for native microalgae cultivation in diluted cow manure digestate.

The application of microalgae to sequester CO2 from flue gases can be an interesting process since it can contribute to mitigate CO2 emission into the atmosphere. One obstacle of such application is the high CO2 concentration in the flue gases, which can lead to low pH in the cultivation medium and hence process failure. This study aims to investigate static CO2 gas supply for microalgae cultivation as a potential alternative that might allow applying different flue gases with different compositions and higher CO2 concentrations. Two sets of experiments were performed. First, the effect of increasing the amount of supplied carbon was tested. In the second experiment, the applicability of such system for different flue gases regarding their oxygen and carbon content was tested. In all experiments, 50 times diluted cow manure digestate was used as a culture medium. By increasing CO2 concentration up to 10% in the supplied air, microalgae growth productivity of 48.7 mg/L/d was achieved. A further improvement of microalgae growth was shown with increasing the gas/culture volume ratio. Microalgae productivity rate increased form 48.7 mg/L/d to 73.5 mg/L/d when the volume of gas increased from 47% to 81% of total volume. Applying CO2 in air (O2 content around 20%) or in N2 (O2 content less than 2%) didn't show any difference regarding inorganic carbon dissolution, pH, ammonium nitrogen removal, CO2 fixation or biomass productivity. Generally, it can be concluded that static gas supply for microalgae cultivation can allow the application of different flue gases from different industries with low or high O2 content and with CO2 concentration as high as 20%. According to our results, a microalgae cultivation system with continuous static gas supply was proposed.

Prediction of leachate quantity and quality from a landfill site by the long short-term memory model.

The long short-term memory (LSTM) model was first applied in this study for the prediction of the leachate quantity and quality at a real landfill site. In our LSTM model, in the learning phase from July 2003 to March 2018, three input data items consisting of the daily precipitation (DP), the daily average temperature (DAT), and the accumulated amount of landfilled waste presented the quantity of leachate generated with high accuracy. The DAT was important for the landfill site, particularly in a snow area because it contributes to the leachate generated during the spring thaw with low precipitation. In the testing phase from April 2018 to March 2019, our LSTM model predicted the leachate generated with a mean absolute percentage error (MAPE) of 26.2%. The concentrations of biological oxygen demand, chemical oxygen demand, total nitrogen, calcium ion and chloride ion in leachate were presented in the learning phase by six input data items: DP, DAT, and the daily amount of landfilled waste (incineration residue, incombustible waste, business waste, and combustible waste) with high R2 values. In the testing phase, the quality of leachate was predicted with the MAPE between 11.8% and 30.2%. Another year data from April 2019 to March 2020 was used to verify accuracy of our model with no overfitting. This study showed the possibility of applying the LSTM model to future predictions of leachate quantity and quality from landfill sites with an acceptable error for daily operation.

Attempts to alleviate inhibitory factors of anaerobic digestate for enhanced microalgae cultivation and nutrients removal: A review.

Anaerobic digestion is a well-established process that is applied to treat organic wastes and convert the carbon to valuable methane gas as a source of energy. The digestate that comes out as a by-product is of a great challenge due to its high nutrient content that can be toxic in case of improper disposal to the environment. Several attempts have been done to valorize this digestate. Digestate has been considered as an interesting medium to cultivate microalgae. The nutrients available in the digestate, mainly nitrogen and phosphorus, can be an interesting supplement for microalgae growth requirement. The main obstacles of using digestate as a medium to cultivate microalgae are the dark color and the high ammonium-nitrogen concentration. The focus of this review is to discuss in detail the major attempts in research to overcome inhibition and enhance microalgae cultivation in digestate. This review initially discussed the obstacles of digestate as a medium for microalgae cultivation. Different processes to overcome inhibition were discussed including dilution, supplying additional carbon source, favoring mixotrophic cultivation and pretreatment. More emphasis in this review was given to digestate pretreatment. Among the pretreatment methods, filtration, and centrifugation were of the most applied ones. These strategies were found to be effective for turbidity and chromaticity reduction. For ammonium nitrogen removal, ammonia stripping and biological pretreatment methods were found to play a vital role. Adsorption could work both ways depending on the material used. Combining different pretreatment methods as well as including selected microalgae stains were found interesting strategies to facilitate microalgae cultivation with no dilution. This study recommend that more study should investigate the optimization of microalgae cultivation in anaerobic digestate without the need for dilution.

Strategy of landfilled waste reduction by a distributed materials recovery facility system in Surabaya, Indonesia.

Slow progress in municipal waste reduction and landfill space scarcity lead to numerous environmental problems in Indonesia and developing countries. Surabaya, the role model of an environmental management city in Indonesia and other countries, is no exception. Despite the situation, Surabaya's initiative of deploying a distributed materials recovery facility (MRF) and its performance in recovering recyclables show a potential to be developed for addressing the landfill waste reduction issues. This study proposes a new strategy with small-sized distributed MRFs to achieve 30% landfilled waste reduction and reducing greenhouse gas (GHG) emissions, focusing on Surabaya as the case study. Scenario 1 merged three pairs of transfer stations which shows some indistinguishable optimizations and failed to meet the target. Both Scenario 2 and Scenario 3 added six years of landfill lifetime for reaching the target. However, the distributed MRF system and different transportation systems in Scenario 3 accomplished the goal with only 24 new MRFs, whereas Scenario 2 needs to upgrade 48 transfer stations into MRFs. Scenario 3 decreased the GHG emissions generation by 29%, possibly contributing to Indonesia's GHG emissions target of 0.2%.

Appropriate conditions for applying NaOH-pretreated two-phase olive milling waste for codigestion with food waste to enhance biogas production.

The high methane gas production potential of two phase olive milling waste (2POMW) makes its application to biogas plants in business an economical process to increase the productivity of the plants. The objective of this study was to investigate the appropriate conditions for the codigestion of NaOH-pretreated 2POMW with food waste. NaOH pretreatment can increase the methane production by increasing the soluble chemical oxygen demand (sCOD), but it may cause inhibition because of higher levels of alkalinity, sodium ion, volatile fatty acids and long chain fatty acids (LCFAs). Therefore, the first experimental phase of this study aimed to investigate the effect of different mixing ratios of 2POMW to food waste. A continuous stirred tank reactor experiment with different mixing ratios of 3%, 4.3%, 5.7% and 8.3% (2POMW: food waste) was conducted. NaOH pretreatment in the range of 6-20% was used. A mixing ratio up to 4.3%, when 10% NaOH pretreatment was used, caused no inhibition and increased methane production by 445.9mL/g-VS(2POMW). For this mixing ratio an additional experimental phase was conducted with the 20% NaOH pretreatment as the 20% NaOH pretreatment had the highest sCOD. The methane gas production was increased by 503.6mL/g-VS(2POMW). However, pH adjustment was required for applying this concentration of the high alkalinity 20% NaOH-pretreated 2POMW. Therefore, we consider using 10% NaOH pretreatment in a mixing ratio of 4.3% to be more applicable. The increase in methane gas production was correlated to the oleic acid concentration inside the reactors. The high oleic acid concentration of 61.8mg/L for the 8.3% mixing ratio was responsible for the strong inhibition. This study showed that adjusting the appropriate mixing ratio of the NaOH-pretreated 2POMW could increase the electricity production of a reactor that regularly receives food waste.

Influence of moisture content, particle size and forming temperature on productivity and quality of rice straw pellets.

A large amount of rice straw is generated and left as much in paddy fields, which causes greenhouse gas emissions as methane. Rice straw can be used as bioenergy. Rice straw pellets are a promising technology because pelletization of rice straw is a form of mass and energy densification, which leads to a product that is easy to handle, transport, store and utilize because of the increase in the bulk density. The operational conditions required to produce high quality rice straw pellets have not been determined. This study determined the optimal moisture content range required to produce rice straw pellets with high yield ratio and high heating value, and also determined the influence of particle size and the forming temperature on the yield ratio and durability of rice straw pellets. The optimal moisture content range was between 13% and 20% under a forming temperature of 60 or 80 °C. The optimal particle size was between 10 and 20mm, considering the time and energy required for shredding, although the particle size did not significantly affect the yield ratio and durability of the pellets. The optimized conditions provided high quality rice straw pellets with nearly 90% yield ratio, ⩾ 12 MJ/kg for the lower heating value, and >95% durability.

Estimation of methane emission rate changes using age-defined waste in a landfill site.

Long term methane emissions from landfill sites are often predicted by first-order decay (FOD) models, in which the default coefficients of the methane generation potential and the methane generation rate given by the Intergovernmental Panel on Climate Change (IPCC) are usually used. However, previous studies have demonstrated the large uncertainty in these coefficients because they are derived from a calibration procedure under ideal steady-state conditions, not actual landfill site conditions. In this study, the coefficients in the FOD model were estimated by a new approach to predict more precise long term methane generation by considering region-specific conditions. In the new approach, age-defined waste samples, which had been under the actual landfill site conditions, were collected in Hokkaido, Japan (in cold region), and the time series data on the age-defined waste sample's methane generation potential was used to estimate the coefficients in the FOD model. The degradation coefficients were 0.0501/y and 0.0621/y for paper and food waste, and the methane generation potentials were 214.4 mL/g-wet waste and 126.7 mL/g-wet waste for paper and food waste, respectively. These coefficients were compared with the default coefficients given by the IPCC. Although the degradation coefficient for food waste was smaller than the default value, the other coefficients were within the range of the default coefficients. With these new coefficients to calculate methane generation, the long term methane emissions from the landfill site was estimated at 1.35×10(4)m(3)-CH(4), which corresponds to approximately 2.53% of the total carbon dioxide emissions in the city (5.34×10(5)t-CO(2)/y).

A needs analysis method for land-use planning of illegal dumping sites: a case study in Aomori-Iwate, Japan.

Land use at contaminated sites, following remediation, is often needed for regional redevelopment. However, there exist few methods of developing economically and socially feasible land-use plans based on regional needs because of the wide variety of land-use requirements. This study proposes a new needs analysis method for the conceptual land-use planning of contaminated sites and illustrates this method with a case study of an illegal dumping site for hazardous waste. In this method, planning factors consisting of the land-use attributes and related facilities are extracted from the potential needs of the residents through a preliminary questionnaire. Using the extracted attributes of land use and the related facilities, land-use cases are designed for selection-based conjoint analysis. A second questionnaire for respondents to the first one who indicated an interest in participating in the second questionnaire is conducted for the conjoint analysis to determine the utility function and marginal cost of each attribute in order to prioritize the planning factors to develop a quantitative and economically and socially feasible land-use plan. Based on the results, site-specific land-use alternatives are developed and evaluated by the utility function obtained from the conjoint analysis. In this case study of an illegal dumping site for hazardous waste, the uses preferred as part of a conceptual land-use plan following remediation of the site were (1) agricultural land and a biogas plant designed to recover energy from biomass or (2) a park with a welfare facility and an athletic field. Our needs analysis method with conjoint analysis is applicable to the development of conceptual land-use planning for similar sites following remediation, particularly when added value is considered.

Centralization of dairy farming facilities for improved economics and environmental quality.

In Japan, most farm animal excreta has been stored directly on farmland. Runoff from this storage has often caused water pollution. Biogasification is anticipated as an important technology to manage excreta properly, but complex problems hinder its introduction. Economic aspects of management have been especially difficult for dairy farmers. For this study, structural problems regarding introduction of biogasification into dairy farming were identified. Subsequently, a desirable system of dairy farming including biogasification was suggested, and an evaluation model of the financial balance was constructed. A case study using current financial balances of several systems of dairy farming was evaluated using the constructed model and actual data. The systems were based on several policy alternatives including the suggested system mentioned above. Results show that a farmer can obtain sufficient income from a system featuring centralization of dairy housing and biogasification facilities and coordinated management by over six farmers.

Estimation of the biodegradation rate of 2,3,7,8-tetrachlorodibenzo-p-dioxin by using dioxin-degrading fungus, Pseudallescheria boydii.

We are developing a bioreactor system for treating dioxin-contaminated soil or water using the dioxin-degrading fungus, Pseudallescheria boydii (P. boydii). In order to design the bioreactor system, this study estimated the rate at which P. boydii degraded 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), which is the most toxic of the dioxins. The experimental results showed that P. boydii degraded 2,3,7,8-TCDD during its logarithmic growth phase, using glucose as a carbon source for growth, and that the growth of P. boydii was not affected by 2,3,7,8-TCDD concentrations usually found at contaminated sites. These results were then used to apply successfully an existing mathematical model to the degradation of 2,3,7,8-TCDD by P. boydii. This allowed an estimation of the rate of degradation of 2,3,7,8-TCDD by P. boydii that can be used in the design of the bioreactor system.

Numerical model for a watering plan to wash out organic matter from the municipal solid waste incinerator bottom ash layer in closed system disposal facilities.

Bottom ash from municipal solid waste incineration (MSWI) is a main type of waste that is landfilled in Japan. The long-term elution of organic matter from the MSWI bottom ash layers is a concern because maintenance and operational costs of leachate treatment facilities are high. In closed system disposal facilities (CSDFs), which have a roof to prevent rainfall from infiltrating into the waste layers, water must be supplied artificially and its quantity can be controlled. However, the quantity of water needed and how to apply it (the intensity, period and frequency) have not been clearly defined. In order to discuss an effective watering plan, this study proposes a new washout model to clarify a fundamental mechanism of total organic carbon (TOC) elution behavior from MSWI bottom ash layers. The washout model considers three phases: solid, immobile water and mobile water. The parameters, including two mass transfer coefficients of the solid-immobile water phases and immobile-mobile water phases, were determined by one-dimensional column experiments for about 2 years. The intensity, period and frequency of watering and other factors were discussed based on a numerical analysis using the above parameters. As a result, our washout model explained adequately the elution behavior of TOC from the MSWI bottom ash layer before carbonation occurred (pH approximately 8.3). The determined parameters and numerical analysis suggested that there is a possibility that the minimum amount of water needed for washing out TOC per unit weight of MSWI bottom ash layer could be determined, which depends on the two mass transfer coefficients and the depth of the MSWI bottom ash layer. Knowledge about the fundamental mechanism of the elution behavior of TOC from the MSWI bottom ash layer before carbonation occurs, clarified by this study, will help an effective watering plan in CSDFs.

Development of bioreactor system for treatment of dioxin-contaminated soil using Pseudallescheria boydii.

We developed a conceptual feasible design of bioreactor system for treatment of dioxin-contaminated soils that uses the dioxin-degrading fungus Pseudallescheria boydii (P. boydii) we had isolated. The dioxin-degradation conditions in bioreactor treatment was established by clarifying the inhibiting factors for the growth of P. boydii using both real contaminated and laboratory prepared soils mixed with fly ash. In addition, ethanol extraction process as post-treatment methods for the remaining dioxins, and the sterilization conditions of P. boydii, i.e., a weakly pathogenic fungus, in the residue was investigated. The better growth conditions of P. boydii were found to be chloride ion concentration of less than 10 g/L and a pH of less than 9. Under these conditions, 7310 pg-TEQ/g of the soil was treated to 2860 pg-TEQ/g by the bioreactor process, and the dioxin concentration was further decreased to 580 pg-TEQ/g by ethanol extraction, resulting to total removal ratio of 92%. Furthermore, development of an effective sterilization method for living P. boydii in the residue increased the applicability of our bioreactor system for practical use in dioxin-contaminated sites.