3.1 Resource efficiency analysis
3.1.1 Analysis of water consumption and wastewater generation
For each ton of cassava starch, the freshwater consumption within the starch production process in scenario 1 used 16.7 m3 of freshwater and generated 19.6 m3 of effluent as show in table 1 and figure 3. The wastewater enters the open lagoon for evaporation. To minimize wastewater sources, wastewater from each processing unit can be reused or recycled based upon its characteristics in the former units, e.g., wastewater from the separating and dewatering units were reused to the extracting and separating unit. The used water from the dewatering unit contained protein impurities and so was not suitable to be reused in the other stages except for root washing [8, 25]. For scenario 2, the freshwater consumption (per ton of cassava starch) was 15.1 m3 of freshwater and 1.6 m3 of recycled water, generating 19.6 m3 of effluent. The wastewater entered the covered lagoon to generate 59.3 m3 of biogas. For scenario 3, the water consumption was 15.1 m3 of freshwater and 1.6 m3 of recycled water to generate 17.6 m3 of effluent. The wastewater entered the covered lagoon to generate 357.8 m3 biogas as show in figure 3.
The biogas from scenario 2 and 3 used to producing heat and electricity in the CSPP. The treated wastewater was discharged into the open lagoon. The factory distributed the treated wastewater for nearby farmers to use as liquid fertilizer .
3.1.2 Analysis of energy consumptions
The electricity consumption of the CSPP was calculated as 197.8 kWh t-1 of starch. For scenario 2, 4.5 kWh t-1 cassava starch produced was required for the biogas system from wastewater, whereas in scenario 3 this was almost 2.6-fold higher at 11.6 kWh t-1 the CSPP as shown in table 1. However, the biogas obtained from the wastewater produced 21.2 kWh of electricity or 2.54 USD t-1, while the biogas production from cassava pulp produced 968.9 kWh of electricity and then be used in the CSPP 176.6 kWh or 21.19 USD t-1 of starch. Therefore, a surplus of 738.4 kWh from scenario 3 was generated and could theoretically be sold to the electricity grid as 88.60 USD t-1 of starch as show in table 1 and figure 3.
The fuel oil used to supply process heat for the flash dryer was evaluated as 1,518.5 MJ. Biogas recovery from the wastewater treatment system has shown great potential for starch factories. Since the price of fuel oil has increased significantly over the past decade, cassava starch factories have been using biogas to replace the fuel oil for the burners to generate hot air for drying the moist starch. The direct burning of the biogas obtained from the wastewater can supply 1,124.2 MJ of energy. Moreover, the biogas from scenario 3 is able to supply 1,724.2 MJ of energy as show in table 1. In conclusion, the fuel oil is unnecessary for thermal energy in the CSPP. The recovered biogas from the wastewater and cassava pulp was used to substitute fuel oil of 29.4 and 15.7 L t-1 of starch and this helped to reduce the fuel cost by approximately 16.49 and 8.80 USD t-1 of starch, respectively, based upon the cost of fuel oil at 0.56 USD L-1 as show in table 1 and figure 3.
3.1.3 Cost reduction
The main production cost in the CSPP is the expenditure on purchasing cassava roots, which makes up to 83-91% of the total costs. The other costs are electricity (3-9%), fuel (4-5%), water (1%), chemicals (4%), and labor (2%) . In this case, the reduction in the fuel oil and electricity from biogas in scenarios 2 and 3 reduced the total costs by 4% and 11%, respectively as show in figure 3.
The scenario 3 has the highest resource efficiency because the conversion of the waste into a biogas (value-added product). Therefore, the electricity and fuel in CSPP was reduced due to the substitution of the energy source by biogas.
3.2 Environmental impact assessment
The CE concept focuses on reducing the landfill, GHG emission, and production energy consumption, while increasing the resource use efficiency and so enabling a new life-cycle for the otherwise end-of-life product. Regarding the minimization of the GHG emissions, the CO2 equivalent from the three scenarios was considered in this study to analyze the GHG emission. From the previous study found that the total GHG emission of cassava starch production was in the range 93.2-935.0 kg CO2eq/FU [14, 26].
In this study, the GHG emission was related to the emissions from electricity consumption, energy consumption, cassava pulp utilization options, and water treatment methods. The CSPP contributed 144.3-636.0 kg CO2eq t-1 (Table 1). Key factors of variations were used different total amounts of electricity, fuel, and water (fresh and recycle water). In the no biogas scenario, the GHG emission of CSPP was higher 3-4 times than that in the biogas scenario because of the higher emissions of methane to atmosphere from the wastewater, the emissions of fossil fuel during combustion, and the higher use of grid electricity. These results mean the GHG emission of CSPP in Thailand was reduced from 2.4 million t of CO2eq y-1 to 0.6-0.8 million t of CO2eq y-1.
Under scenario 3, the cassava starch industry applied the CE concept, including a covered lagoon for biogas generation from wastewater and a CSTR for biogas generation from the cassava pulp, reducing the GHG emission by 77% as shown in figure 4. This result was achieved by the reduced electricity consumption from the electricity grid and the reduced GHG emission from wastewater treatment using anaerobic technology.
3.3 Land use
The three scenarios were also examined for their effect on the land utilization. For a cassava starch factory with a process capacity of 500 t d-1, the land use options are the construction of a 1.6 ha starch production plant, 14.5 ha wastewater treatment (covered lagoon), 1.8 ha CSTR for biogas production from cassava pulp, and 44.3 ha for drying the cassava pulp. The total land use areas for scenarios 1, 2, and 3 were 59.2, 47.2, and 18.9 ha, respectively. The land needs are significantly reduced for scenario 3 due to the reduction of the cassava pulp drying area and open pond for wastewater treatment.
3.4 Economic impact
The economic viability and the IRR are the main factors of concern to any entrepreneur, and the first stage that entrepreneurs will calculate is total investment cost. The investment cost of a biogas system depends on type of feedstock and biogas conversion technology. The relationship between the investment time and biogas conversion technology providesa measurement of the corresponding effect in terms of investment timing. For this, the NPV is the economic analysis method that best assesses the investment cost of a biogas system.
As outlined already, cassava pulp can be utilized in many ways, such as the animal feed, and a carbon source in an alcohol fermentation process. However, the factories are not entirely satisfied with the current cassava pulp utilization and disposal options because the cassava pulp still has high starch content, which they view as a loss to them, even though odor is a constant problem. Biogas generation from cassava pulp is one option to solve these problems [5, 16].
The investment cost varied with the size of reactor and the organic loading rate to the system (kg COD m3 of digester d-1). The investment and operation costs of the CSTR technology were 180.00-267.00 USD m-3 biogas system and 0.07-0.17 USD m-3 wastewater, respectively . In this study, the investment cost of the biogas production system consisted of land (10-25%), reactor system (18-35%), piping (5-13%), purification system (8-12%), generator (15-29%), and other (e.g., insulation and equipment installation). The key economic indicators for a biogas system from wastewater and cassava pulp are presented in Table 2. For the biogas generation from scenarios 2 and 3, the total investment cost was 2.24 and 8.65 million USD, respectively. The payback period for biogas generation from scenario 3 was the most economically attractive option due to the highest NPV of 6.15 million USD with a payback period of 4.37 y.
3.5 Drivers and barriers of CE concept implementation for the CSPP
This study determined which four main factors that were technical, economic, regulatory, and social responsibility as a driver or a barrier for CE concept implementation in the CSPP. A driver was defined as a supporting factor and a barrier was defined as an inhibiting factor to implementation of the CE concept using the wastewater and cassava pulp to produce biogas for producing heat and electricity in factories.
The results showed that the main driver and barrier for CE concept implementation in the CSPP were technical concerning. The regulatory factors were the most important concern to entrepreneurs (36%), followed closely by economic factors (35%) and then social responsibility and technical support at 21 and 8%, respectively. For the barriers to CE concept implementation technical problems were the most important factor that concerned entrepreneurs (35%), followed by regulatory, economic, and social at 23%, 22%, and 20%, respectively [27, 28]. The driver and barrier of CE concept implementation are as show in table 3.
The technical barriers are outlined in turn below.
184.108.40.206 Limitations of pretreatment technology
The application of biogas production from cassava pulp still has technical and cost-effectiveness limitations. Technically, the cassava pulp has high lignocelluloses so these are difficult to convert into biogas. It requires both a long retention time inside the biogas reactor and an equally large reactor size [19, 29]. The pretreatment process to increasing surface area of cassava pulp, increasing microorganism accessibility, increasing substrate digestibility, and increasing lignin and hemicellulose solubility might be required [13, 30]. Currently, the total degradation time for the solid organic waste is approximately 30 d.
220.127.116.11 Availability of cassava pulp
The amount of energy produced from biogas varies with the volume of cassava pulp generated by the factory, making it difficult to manage the energy. Cassava pulp is an agricultural residue that is available only during the cassava root harvesting period (September to April), is difficult to store, and so it is sometimes left on the biogas generation site for mulching purposes . Biogas production systems that support a wide range of raw materials and substrates would enhance the investment opportunities for biogas production systems and satisfy the desire of the electricity utility for year-round generation. More work needs to be done on developing such systems.
18.104.22.168 Lack of a successful model for biogas production from cassava pulp
A modified covered lagoon is the most popular system chosen by investors for processing cassava pulp due to the stability of the system. Furthermore, the system is able to support the fluctuation/variance of wastewater/solid waste in each production season, does not have a very high investment cost and is relatively easy for operation and maintenance. Yet the system requires large land area. However, most starch factories are not confident in the efficiency of the high technology for biogas system generation from cassava pulp, since the technology has not yet been established at the commercial scale, nor shown to be cost-effective. Too few models of success to establish the efficiency of this biogas technology are available to satisfy the doubts of potential investors.
Economic barriers to CE concept implementation for the CSPP are related to the cost-effectiveness, uncertain return and profit, and lack of incentive.
22.214.171.124 Financial barriers
The biogas investment and operation cost was approximately 6.00-1000.00 USD m-3 and 0.02-2.67 USD m-3 of wastewater respectively, ranging from a simple lagoon to high technology biogas system with pretreatment technology. It can be seen that the more complex the technology, the higher the operating cost. The cost depends not only on the chosen technology, but also the type of feedstock [19, 30]. Therefore, biogas production from the cassava pulp requires a pretreatment step to adjust the physical and chemical properties, which results in higher biogas production costs and investment costs.
Current benefit measures provided by the government, such as tax benefits and financial support, are too little to motivate entrepreneurs to invest more in building biogas systems. Added to this is the difficulty of paperwork when requesting funding for an extension of the support limit, for permits, and for licenses, which often involve different agencies. Thus, the associated bureaucracy needs to be made easier.
126.96.36.199 Lack of incentive
Government policies, especially the announcement to stop accepting claims and proposals to sell electricity from very small power producers that generate electricity from RE, is causing a slowdown in investment and is of great concern to the entrepreneurs who have already invested in biogas power generation systems. In addition, the current electricity purchase price is close to the production cost, making the PBP longer, and so far less attractive for the private sector to invest in. This is because the Ministry of Energy estimates that current electricity reserves are about 30% . The termination of financial assistance, especially for the cases of waste and wastewater without efficient technology, is a major obstacle causing the private sector to cancel or delay the decision to invest in biogas production systems. Although there is an overall policy to promote energy from renewable resources, the denial of new feed-in tariff (FiT) approvals is possibly the greatest barrier to investment. It not only denies an increase in the use of renewable resources, it runs counter to CE concept implementation.
Environmental regulations are one of the drivers of CE concept implementation for the CSPP related to the reduction of GHG emission. Since laws require expensive policing and civil actions, voluntary compliance under social responsibility would be preferable .
188.8.131.52 Agreement on GHG emissions in COP24
From COP24, Thailand signed an agreement on the implementation of the guidelines of the Paris Agreement to reduce its GHG emission by 20% below the 2010 emission levels by 2030. Environmental policies have been set up, such as the Environmentally Sustainable Transport System Plan, a Waste Management Roadmap, FiT, and tax incentives, to promote investment in RE [31, 32].
184.108.40.206 Laws on waste and wastewater treatment
Hazardous Waste Management laws define cassava pulp as a hazardous waste so it is prohibited to transport it off-site. This results in the disturbing odors and the need for landfill for drying the cassava pulp.
In terms of barriers, the primary disincentives are the high initial investment costs, lack of a conducive legal system, limited government support, especially in power purchase and production of RE, as well as a conflict in the laws on waste management and product lifecycle management. These are outlined in turn below.
220.127.116.11 Lack of a conducive legal system
The government attaches great importance to the development of the country into the CE. However, this top down policy has not been integrated into the actual production stream with any unity. By way of example, investment in biogas systems still requires contacting several departments, either sub-district administration organizations, provincial industry authorities, Department of Industry, Department of Business Development, Department of Alternative Energy Development and Energy Conservation, local power authorities, local environment authorities, and the Energy Regulatory Office.
18.104.22.168 Limited government support
Policy/law/regulation in RE and the environment is unclear and highly changeable in biogas production systems. Thailand has the policies and strategies in place associated with a sustainable development, environment, and energy, including the implementation of the Sustainable Development Agenda B.E. 2030, (Sustainable Development Goals: SDGs), the AEDP was updated in 2018 to focus on bio, circular, and green economy . However, the various promotional measures focus on the economic returns and determination of the purchase price of RE is mainly based on the lowest cost of energy.
22.214.171.124 Conflict of laws on waste management on product lifecycle management
The Urban Planning Act stipulates that biogas projects are on a negative list and so cannot be co-located with raw material production sources (e.g., cassava starch factories and palm oil plants). Currently, the Ministry of Industry is in the process of listening to public opinion to solve this issue of the urban plan problem as it is also associated with the request for borrowing funds from the bank by the developer.
3.5.4 Social responsibility
Social responsibility is driven by CE concept implementation in the cassava starch industry related to the area of the industry. These are discussed below
126.96.36.199 Expansion of communities close to industry
With the high demand for living space, communities are expanding closer to the cassava processing factories, which, when first established, were relatively isolated. This is largely due to a lack of proper zoning from the outset. Communities are of course concerned about the detrimental environmental effects of industry and are active in their surveillance and reporting to the government. This result in an important driving force for investment in the CE concept and minimization of emissions and waste.
The current barriers are associated with the lack of environmental concern from entrepreneurs.
188.8.131.52 Lack of environmental concern
Thailand’s environmental laws have only been set for sewage measures. Therefore, entrepreneurs are not interested in investing in high-efficiency biogas production systems that require a high investment. This is in contrast to foreign countries, such as Germany and Italy, who have implemented measures to support/attract the use of more modern technology.
Therefore, Thailand should establish a network, including the enforcement of environmental laws, and improve related laws to be in the same direction. Environmental crime punishment, surveillance, and reporting are important driving forces for investment in biogas production systems. This would include the establishment of an organization to disseminate knowledge, including making policy recommendations that promote and support the construction of biogas production systems in accordance with space and industry limitations. In addition, for effective operations, the government needs to establish a mechanism for monitoring and disseminating biogas performance to the public.