Wastewater-based resource recovery technologies across scale: A review

Over the past few decades, wastewater has been evolving from a waste to a valuable resource. Wastewater can not only dampen the effects of water shortages by means of water reclamation, but it also provides the medium for energy and nutrient recovery to further offset the extraction of precious resources. Since identifying viable resource recovery technologies can be challenging, this article offers a review of technologies for water, energy, and nutrient recovery from domestic and municipal wastewater through the lens of the scale of implementation. The system scales were classified as follows: small scale (design flows of 17 m3/day or less), medium scale (8 to 20,000 m3/day), and large scale (3800 m3/day or more). The widespread implementation of non-potable reuse (NPR) projects across all scales highlighted the ease of implementation associated with lower water quality requirements and treatment schemes that resembled conventional wastewater treatment. Although energy recovery was mostly achieved in large-scale plants from biosolids management or hydraulic head loss, the highest potential for concentrated nutrient recovery occurred in small-scale systems using urine source separating technologies. Small-scale systems offered benefits such as the ability for onsite resource recovery and reuse that lowered distribution and transportation costs and energy consumption, while larger scales benefited from lower per unit costs and energy consumption for treatment. The removal of pharmaceuticals and personal care products remained a challenge across scales, but unit processes such as reverse osmosis, nanofiltration, activated carbon, and advanced oxidation processes exhibited high removal efficiency for select contaminants.