Abstract
Limits in resource availability are driving a change in current societal production systems, changing the focus from residues treatment, such as wastewater treatment, toward resource recovery. Biotechnological processes offer an economic and versatile way to concentrate and transform resources from waste/wastewater into valuable products, which is a prerequisite for the technological development of a cradle-to-cradle bio-based economy. This review identifies emerging technologies that enable resource recovery across the wastewater treatment cycle. As such, bioenergy in the form of biohydrogen (by photo and dark fermentation processes) and biogas (during anaerobic digestion processes) have been classic targets, whereby, direct transformation of lipidic biomass into biodiesel also gained attention. This concept is similar to previous biofuel concepts, but more sustainable, as third generation biofuels and other resources can be produced from waste biomass. The production of high value biopolymers (e.g., for bioplastics manufacturing) from organic acids, hydrogen, and methane is another option for carbon recovery. The recovery of carbon and nutrients can be achieved by organic fertilizer production, or single cell protein generation (depending on the source) which may be utilized as feed, feed additives, next generation fertilizers, or even as probiotics. Additionlly, chemical oxidation-reduction and bioelectrochemical systems can recover inorganics or synthesize organic products beyond the natural microbial metabolism. Anticipating the next generation of wastewater treatment plants driven by biological recovery technologies, this review is focused on the generation and re-synthesis of energetic resources and key resources to be recycled as raw materials in a cradle-to-cradle economy concept.
Highlights
FROM WATER REMEDIATION TO WATER MINING: CRADLE-TO-CRADLE IN WASTEWATERThe current societal production system, based on raw matter extraction and industrial transformation into products, has longterm sustainability issues (Lovins, 2008)
Those technologies derived from biomining activities are linked to mobilization of metals, whereas technologies adapted from bioremediation techniques are more associated with immobilization of metals
There are some detailed reviews showing a big picture on metals recovery (Kikuchi and Tanaka, 2012; Johnson, 2014; Nancharaiah et al, 2016) but in this part the novelest and most impacting studies in recent dates are analyzed based on their link with the circular economy concept
Summary
The current societal production system, based on raw matter extraction and industrial transformation into products, has longterm sustainability issues (Lovins, 2008). We are entering the start of another major cycle, driven partly by the end of life of the current infrastructure, as well as by recognition of a need to reduce global environmental impact and enable long term societal sustainability (Verstraete et al, 2009; Mccarty et al, 2011; Batstone et al, 2015) This aims at reducing the substantial resource consumption (energy, chemicals, and transport) of existing wastewater treatment and enabling instead recovery of the value inherent in wastewater (Daigger, 2009). This was further developed, as the “partition-release-recover” process, which uses biological agents to selectively remove nutrients and carbon from the liquid phase (Batstone et al, 2015) This is a combined and scalable process, able to treat wastewater at essentially zero energy input, and recover nitrogen, phosphorous, and potentially, value-added organics or microbial products from the effluent. Three enable the generation of value-added products in the form of biomass (and other byproducts) that represent enabling platforms for resource recovery
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