Pre- and post-treatment assessment for the anaerobic digestion of lignocellulosic waste: P-graph

Lignocellulosic waste is one of the most abundant and potential feedstocks for anaerobic digestion (AD), but the energy efficiency is limited by the lignocellulosic composition which is recalcitrant to biodegradation. Pretreatment of feedstock and the post-treatment of biogas and digestate play a significant role in enhancing the AD efficiency as well as the product utilisation. This study aims to determine the cost-optimal pre-and post-treatment pathway for an AD of lignocellulosic waste by applying P-graph. The economic balance between the main operating cost, yield and quality of products were considered. The treatment options were overviewed followed by a case study considered a different combination of physical, chemical and biological pretreatments, biogas post-treatment (combine heat and power, fuel cell, biomethane, biofuel) and digestate treatments. A total of 9 pre-treatments for lignocellulosic waste, 2 digestate post-treatments and 9 post-treatments for biogas were evaluated in this study. Chemical pre-treatment by CaO, post-treatment by H2S removal with membrane separation for biomethane production and without the composting of digestate is suggested as the optimal treatment pathway for lignocellulosic waste

Regional renewable energy and resource planning

The exploitation of the energy potential in biomass in a specific geographical region is frequently constrained by high production costs and the amount of land required per unit of energy generated. In addition, the distributed nature of the biomass resource and its normally low energy density may result in large transportation costs. Biomass also requires large land areas to collect and process the incoming solar radiation before the energy can be harvested. Previously published works on regional energy clustering (REC) and the Regional Resources Management Composite Curve, RRMCC (in this paper shortened to RMC), have been extended in this paper to tackle simultaneously the issues of the biomass supply chain, transportation, and land use. The RMC is a tool for supporting decision making in regional resource management. It provides a complete view of energy and land availability in a region, displaying their trade-offs in a single plot. The extension presented in this work has been developed in two steps. The first step presents the Regional Energy Cascade Analysis, which estimates the energy target within regional supply chains and provides the result for energy exchange flows between zones, the quantity of energy required to be imported/exported, and the locations of the demands. In the second step, the initial results are analysed against potential measures for improving the energy and land use targets by using the RMC and a set of rules for its manipulation. The presented method provides the option to assess the priorities: either to produce and sell the surplus energy on the fuel market or use the land for other purposes such as food production. This extended approach is illustrated with a comprehensive case study demonstrating that with the RMC application it is possible to maximise the land use and to maximise the biofuel production for the requested energy demand.Renewables Regional energy clustering Biomass supply chain Regional Energy Cascade Analysis Resource planning Carbon footprint minimisation

Maximizing total site water reuse via a two-way centralized water header

Water is widely used in industry for processes such as washing, stripping, extraction, heating and cooling. Water minimization has become an urgent need in industry due to the scarcity of quality water, stricter environmental regulations, rising price of freshwater as well as the cost of wastewater treatment. In some countries and regions, water is more important than energy. Even though there have been numerous research works on Total Site Water Integration, the methodologies may still need further development from aspects of practical implementation. Superstructures considering all possibilities of water exchange among sources and demands in industrial sites typically result in complex industrial water networks that may be practically very challenging to implement due to plant layout and economic constraints as well as coordination issues. Total Site Centralized Water Integration is developed to address these issues through the use of a centralized water reuse header. In this paper, a U-shaped, two-way centralized water reuse header is designed to improve the Total Site water exchange. As compared to a one-way centralized water reuse header the minimum freshwater requirement for the two-way centralized water reuse header further reduces fresh water requirement from 51.8% to 56.2% and wastewater generation, from 51.5% to 55.9%. The two-way header also reduces the payback period from 5 to 4.7 y

Effect of compost maker on composting and compost quality

Compost and its liquid product can be used as an organic fertiliser. Bulking agent, microbial inoculants or compost maker can be added to improve the composting process. Compost maker is an organic substance that speeds up the composting process. It contains microorganisms that can speed up the degradation process and reduce the odour emitted during composting. Limited studies have reported the effect of compost maker on composting and its end quality. The aim of the study is to characterise the nutrient characteristics of the food waste compost treated with compost maker. The correlation between the nutrients in compost and its bio-liquid was investigated. A two-stage composting system, i.e. facultative and aerobic system, will be used. The raw materials used for composting included the post-consumed food waste, shredded palm leaves as the bulking agent and matured compost as the compost maker. Two formulations were conducted: (i) food waste composted with the shredded palm leaves and compost maker using the ratio of 2:1:1 and (ii) food waste composted with the shredded palm leaves (1:1) without the presence of compost maker as the control. The results showed that the first formulation reported the higher contents in nitrogen and potassium as compared to the control. The macronutrients of the solid compost are positively correlated with the respective bio-liquid fertiliser. The use of compost maker is recommended as a supplement to improve the quality of both the solid and liquid compost product

Peak-off-peak load shifting for optimal storage sizing in hybrid power systems using Power Pinch Analysis considering energy losses

The difference in electricity pricing based on the time of power use has led to load shifting from peak to off-peak hours in hybrid power systems (HPS). Apart from optimising electricity cost, shifting of the load may also change the capacity of storage in the system. Power Pinch Analysis has been recently applied to guide load shifting aiming to minimise the cost of electricity, considering the peak and off-peak electricity pricing. The HPS was assumed to be ideal with 100% efficiency, which is not achievable in actual operational condition. This work extends the study by scrutinising the effects of peak-off-peak load shifting on the capacity of storage in HPS. The effects of energy losses due to the inefficiency during power conversion, transfer and storage in the HPS are considered in developing shifting heuristics to ensure optimal storage size is achieved. Implementation of the proposed load shifting strategy on a case study demonstrates that a reduction of up to 30% in the storage size can be achieved, which led to a minimum storage cost. The distribution of peak hours’ demand to off-peak hours also successfully provide significant savings in the electricity bill