Coffee is an important agricultural commodity that is branded according to its environmental criteria in the global market. Therefore, Indonesia’s coffee production system needs to be investigated to meet the demand for eco-labeling, which has become a consumer preference. This study aims to assess the comprehensive sustainability evaluation of coffee production nurtured by an organic fertilizing system (OFS), chemical-organic fertilizing system (COFS), and chemical fertilizing system (CFS) that focuses on the energy–environment–economic nexus. A life cycle assessment (LCA), life cycle cost analysis (LCC), and energy analysis were performed as methods to evaluate the environmental impact, economic performance, and energy requirement analysis. The results indicated that the OFS had superior performance in two sustainability aspects: resulting in the lowest environmental damage and generating the highest economic benefit. Simultaneously, COFS shows the highest sustainability performance as it consumes the least energy. In contrast, CFS indicated the lowest sustainability performance in all aspects: highest environmental impact, lowest economic benefit, and highest energy consumption. Therefore, OFS is strongly recommended to be applied broadly, considering its environmental and economic superiority. Consequently, massive OFS application was followed by higher energy consumption. Alternatively, COFS can be considered for application due to its higher energy performance, even though it can potentially result in higher environmental damage and lower economic benefit. However, the government should explicitly provide some effort for the broad application of OFS in financial and assistance support since the shifting process needs more time to adapt.

A comparative evaluation of energy requirement and CO₂ emission was performed for native polyculture microalgae oil production in a wastewater treatment plant (WWTP). The wastewater provided nutrients for algae growth. Datasets of microalgae oil production and their details were collected from the Minamisoma pilot plant. Environmental impact estimation from direct energy and material balance was analyzed using SimaPro^® v8.0.4. in two scenarios: existing and algal scenarios. In the existing scenario, CO₂ emission sources were from wastewater treatment, sludge treatment, and import of crude oil. In the algal scenario, CO₂ emission with microalgae production was considered using wastewater treatment, CO₂ absorption from growing algae, and hydrothermal liquefaction (HTL) for extraction, along with the exclusion of exhausted CO₂ emission for growing algae and use of discharged heat for HTL. In these two scenarios, 1 m³ of wastewater was treated, and 2.17 MJ higher heating value (HHV) output was obtained. Consequently, 2.76 kg-CO₂ eq/m³-wastewater in the existing scenario and 1.59 kg-CO₂ eq/m³-wastewater in the algal scenario were calculated. In the HTL process, 21.5 MJ/m³-wastewater of the discharged heat energy was required in the algal scenario. Hence, the efficiency of the biocrude production system will surpass those of the WWTP and imported crude oil.

In this study, three paddy harvesting systems, manual harvesting of paddy (MHP), reaper harvesting of paddy (RHP), and combine harvesting of paddy (CHP), were evaluated considering field capacities, field efficiencies, time and fuel consumption, mechanization indices, greenhouse gas emissions, straw availability, and direct and indirect costs. Field experiments were conducted in the North Central Province of Sri Lanka. The effective field capacity, field efficiency and fuel consumption of the combine harvester were 0.34 hah⁻¹, 60.8%, and 34.1 Lha⁻¹, respectively, and those of the paddy reaper were 0.185 hah⁻¹, 58.2%, and 3.8 Lha⁻¹, respectively. The total time consumed by MHP, RHP, and CHP were 76.05 hha⁻¹, 39.76 hha⁻¹, and 2.94 hha⁻¹, respectively. The highest energy utilization was recorded by the CHP, at 1851.09 MJha⁻¹, while MHP recorded the lowest at 643.20 MJha⁻¹. The direct cost of the MHP was 1.50 and 1.52 times higher than those of the CHP and RHP, respectively. MHP recorded the lowest greenhouse gas emissions (32.94 kgCO₂eqha⁻¹), while CHP recorded the highest (176.29 kgCO₂eqha⁻¹). The RHP exhibited an intermediate level in all aspects. Although the CHP has higher field performance and direct costs, it has higher GHG emissions and indirect costs. Therefore, an optimum level of mechanization should be introduced for the long-term sustainability of both the environment and farming.

A comparative evaluation of economic efficiency was performed for native polyculture microalgae oil production in an oxidation ditch (OD) process wastewater treatment plant (WWTP). A cost function was developed for the process. The operational cost per 1 m³ of wastewater (w.w.) was 1.34 $/m³-w.w. in the existing scenario, 1.29 $/m³-w.w. in algal scenario A (no cost for CO₂ and waste heat) and 1.36 $/m³-w.w. in algal scenario B (no cost for CO₂). The conditions were set as follows: hydraulic retention time (HRT): 4 days, microalgal productivity: 0.148 g/L and daily treatment volume: 81.6 m³-w.w./d. The cost differences were related to the increase in polymer flocculants for algae separation (+0.23 $/m³-w.w), carbon credits from CO₂ absorption (−0.01 $/m³-w.w), the sales of biocrude (−0.04 $/m³-w.w) and sludge disposal (−0.18 $/m³-w.w). Hence, the introduction of the algae scenario was the same cost-effective as the existing scenario. Microalgae oil production in an OD process WWTP can serve as a new energy system and reduce the environmental load in a society with a declining population.