Abstract. The production process of indigofera plants yields 10% of blue natural dyes and wastes are 90%.The biomass wastes from the extraction of indigofera plants are classified as difficult to process in an Anaerobic Digester (AD) because of the large content of hemicellulose in the Indigofera stems. Therefore, the study reports the anaerobic digestion of Indigofera plant wastes co-digested with cow dung for enhancing the biogas quality. The digestion process was conducted in a vessel of 160 L with various weight ratios between Indigofera biomass and cow dung by 0%, 25%, 50%, 75%, and 100%. The results show that the AD reactor temperature kept above 29.5°C with a pH between 6-7 were the key factors for enhancing the biogas quality. The co-digestion between 50% indigofera wastes with 50% cow dung yielded biogas with a CH4 content of about 42% and H2S concentration below 40 ppm showing that the biogas has the potential to be further improved in quality and can be used to fuel the stove and power generation.

The rate of development growth in Indonesia has resulted in an increase of energy demand. In addition, most power generation systems still use fossil fuels of nearly 50%, in other words this fuel can run out within the next 18 years. The electricity needs in the building come from the use of lighting, computers, office equipment, heating, ventilation, air conditioning and also air conditioning systems (AHU). This paper aims to investigate energy efficiency based on cooling load capacity to reduce energy use and design an air conditioning system. A well-designed HVAC system will have a great impact on indoor air conditions. Room comfortability will be realized throughout the year and also the outside environment if cared for properly according to the procedures of the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Handbook of Fundamentals. Mastek Mosque required 167,151,241 Btu/h. The ducting design for central air conditioning systems uses 12 x 8 pipes for the main ducting and 10 x 6 for the ducting suction with 12 nozzles and 10 x 6 and 10 x 8 return ducting sizes. This system has the advantages of efficient, silent cooling and increased comfort for prayer.