This recent journal article in Nature,  Sustainable wastewater reuse for agriculture  highlights the importance of using treated wastewater for agriculture. The article describes this opportunity as requiring technological solutions, along with sound regulatory frameworks.

Wastewater is an untapped resource of valuable water and nutrients. Less than 20% of wastewater is treated globally, significantly less used for agricultural irrigation, with most discharged into the nearest water body. Unfortunately, we don't make it easy for ourselves, re-use systems risk chemical contamination from both industry and pharmaceuticals, especially where WWTP's are centralised, and removal of contaminants is required for reuse.

My view is that until researchers connect with real world innovators and practitioners to come up with low cost practical solutions for all scales, treated wastewater implementation will continue to remain low.  Conventional biological processes (activated sludge and anaerobic sludge digestion) and associated sludge management, conceptually make no sense to me. I'd argue that disinfection doesn't either.

The system needs a reset so treated wastewater is fit for purpose and delivered to site at low cost. In my view recirculating, trickling biological filters ("active" vermifilters) are the way forward at all scales. The rule is "keep it simple and safe" (KISS)... and circular. "Advanced" technologies don't need to be complicated.

The total volume of wastewater alone produced globally could satisfy nearly all irrigation water needs. Unfortunately paradigms tend to fall slowly, and then only from the weight of repeated failure.