Integrated life cycle assessment of biotreatment and agricultural use of domestic organic residues: Environmental benefits, trade-offs, and impacts on soil application.

Extensive agricultural activities have been shown to degrade soils, promoting research into improving soil quality. One such method is to increase the amount of organic matter in the soil, and domestic organic residues (DOR) are commonly used for this purpose. The environmental impact of DOR-derived products, from production to agricultural application, remains unclear in current research. With the aim to have a more comprehensive understanding of the challenges and opportunities in DOR management and reuse, this study extended the boundaries of Life Cycle Assessment (LCA) to include the transport, treatment, and application of treated DOR on a national level while also quantifying soil carbon sequestration that has been less addressed in relevant LCA studies. This study focuses on The Netherlands, where incineration predominates, as a representative case to explore the benefits and trade-offs of moving towards more biotreatment for DOR. Two main biotreatments were considered, composting and anaerobic digestion. The results indicate that biotreatment of kitchen and yard residues generally has higher environmental impacts than incineration, including increased global warming and fine particulate matter formation. However, biotreatment of sewage sludge has lower environmental impacts than incineration. Substitution of nitrogen and phosphorus fertilisers with compost reduces mineral and fossil resource scarcity. In fossil-based energy systems like The Netherlands, replacing incineration with anaerobic digestion yields the highest benefit for fossil resource scarcity (61.93 %) due to energy recovery from biogas and the predominant use of fossil resources in the Dutch energy system. These findings indicate that replacing incineration with biotreatment of DOR may not benefit all impact categories in LCA. The environmental performance of substituted products can significantly influence the environmental benefits of increased biotreatment. Future studies or implementation of increased biotreatment should consider trade-offs and local context.

Influence of Cell Configuration and Long-Term Operation on Electrochemical Phosphorus Recovery from Domestic Wastewater.

Phosphorus (P) is an important, scarce, and irreplaceable element, and therefore its recovery and recycling are essential for the sustainability of the modern world. We previously demonstrated the possibility of P recovery by electrochemically induced calcium phosphate precipitation. In this Article, we further investigated the influence of cell configuration and long-term operation on the removal of P and coremoved calcium (Ca), magnesium (Mg), and inorganic carbon. The results indicated that the relative removal of P was faster than that of Ca, Mg, and inorganic carbon initially, but later, due to decreased P concentration, the removal of Ca and Mg became dominant. A maximum P removal in 4 days is 75% at 1.4 A m-2, 85% at 8.3 A m-2 and 92% at 27.8 A m-2. While a higher current density improves the removal of all ions, the relative increased removal of Ca and Mg affects the product quality. While the variation of electrode distance and electrode material have no significant effects on P removal, it has implication for reducing the energy cost. A 16-day continuous-flow test proved calcium phosphate precipitation could continue for 6 days without losing efficiency even when the cathode was covered with precipitates. However, after 6 days, the precipitates need to be collected; otherwise, the removal efficiency dropped for P removal. Economic evaluation indicates that the recovery cost lies in the range of 2.3-201.4 euro/kg P, depending on P concentration in targeted wastewater and electrolysis current. We concluded that a better strategy for producing a product with high P content in an energy-efficient way is to construct the electrochemical cell with cheaper stainless steel cathode, with a shorter electrode distance, and that targets P-rich wastewater.

Production of Caproic Acid from Mixed Organic Waste: An Environmental Life Cycle Perspective.

Caproic acid is an emerging platform chemical with diverse applications. Recently, a novel biorefinery process, that is, chain elongation, was developed to convert mixed organic waste and ethanol into renewable caproic acids. In the coming years, this process may become commercialized, and continuing to improve on the basis of numerous ongoing technological and microbiological studies. This study aims to analyze the environmental performance of caproic acid production from mixed organic waste via chain elongation at this current, early stage of technological development. To this end, a life cycle assessment (LCA) was performed to evaluate the environmental impact of producing 1 kg caproic acid from organic waste via chain elongation, in both a lab-scale and a pilot-scale system. Two mixed organic waste were used as substrates: the organic fraction of municipal solid waste (OFMSW) and supermarket food waste (SFW). Ethanol use was found to be the dominant cause of environmental impact over the life cycle. Extraction solvent recovery was found to be a crucial uncertainty that may have a substantial influence on the life-cycle impacts. We recommend that future research and industrial producers focus on the reduction of ethanol use in chain elongation and improve the recovery efficiency of the extraction solvent.

Bioelectrochemical systems: an outlook for practical applications.

Bioelectrochemical systems (BESs) hold great promise for sustainable production of energy and chemicals. This review addresses the factors that are essential for practical application of BESs. First, we compare benefits (value of products and cleaning of wastewater) with costs (capital and operational costs). Based on this, we analyze the maximum internal resistance (in mΩ m(2) ) and current density that is required to make microbial fuel cells (MFCs) and hydrogen-producing microbial electrolysis cells (MECs) cost effective. We compare these maximum resistances to reported internal resistances and current densities with special focus on cathodic resistances. Whereas the current densities of MFCs still need to be increased considerably (i.e., internal resistance needs to be decreased), MECs are closer to application as their current densities can be increased by increasing the applied voltage. For MFCs, the production of high-value products in combination with electricity production and wastewater treatment is a promising route.

Renewable sustainable biocatalyzed electricity production in a photosynthetic algal microbial fuel cell (PAMFC).

Electricity production via solar energy capturing by living higher plants and microalgae in combination with microbial fuel cells are attractive because these systems promise to generate useful energy in a renewable, sustainable, and efficient manner. This study describes the proof of principle of a photosynthetic algal microbial fuel cell (PAMFC) based on naturally selected algae and electrochemically active microorganisms in an open system and without addition of instable or toxic mediators. The developed solar-powered PAMFC produced continuously over 100 days renewable biocatalyzed electricity. The sustainable performance of the PAMFC resulted in a maximum current density of 539 mA/m2 projected anode surface area and a maximum power production of 110 mW/m2 surface area photobioreactor. The energy recovery of the PAMFC can be increased by optimization of the photobioreactor, by reducing the competition from non-electrochemically active microorganisms, by increasing the electrode surface and establishment of a further-enriched biofilm. Since the objective is to produce net renewable energy with algae, future research should also focus on the development of low energy input PAMFCs. This is because current algae production systems have energy inputs similar to the energy present in the outcoming valuable products.

Energy recovery from controlled mixing salt and fresh water with a reverse electrodialysis system.

The global potential to obtain clean energy from mixing river water with seawater is considerable. Reverse electrodialysis is a membrane-based technique for direct production of sustainable electricity from controlled mixing of river water and seawater. It has been investigated generally with a focus on obtained power, without taking care of the energy recovery. Optimizing the technology to power output only, would generally give a low energetic efficiency. In the present work, therefore, we emphasized the aspect of energy recovery. No fundamental obstacle exists to achieve an energy recovery of > 80%. This number was obtained with taking into account no more than the energetic losses for ionic transport. Regarding the feasibility, it was assumed to be a necessary but not sufficient condition that these internal losses are limited. The internal losses could be minimized by reducing the intermembrane distance, especially from the compartments filled with the low-conducting river water. It was found that a reduction from 0.5 to 0.2 mm indeed could be beneficial, although not to the expected extent. From an evaluation of the internal losses, it was supposed that besides the compartment thickness, also the geometry of the spacer affects the internal resistance.