#Nutrient19
As always, the past 2019 WEF nutrient removal and recovery symposium Minneapolis has once again updated al current and recent developments in this particular field of water treatment. The most relevant features as personally experienced can be summarized as follows:
1. Phosphate recovery by struvite formation should be seen in the broader picture of overall P management and will there fore be dependent on the specific needs related to the treatment plant in question. The actual drivers for implementing any type of struvite treatment are not only the recovery of P as pure fertilizer. The fertilizer properties are equally maintained when sequestering the phosphorus as struvite in the biosolids. Most global phosphate management issues are now clearly defined and do not relate to fertilizer properties of struvite at all. So even if struvite would have no fertilizer properties at all, the process of struvite formation can still be used to govern those phosphate related issues and hypothetically thus generating a useless inert mineral.
2. The sludge digester is the key feature involved in this overall P management. It does contain a dynamically evolving struvite quantity, which can either increase but also decrease having a pronounced influence on the mass quantity of the soluble mobile P fraction wondering around the treatment plant. So again, form a global phosphate management point of view stripping phosphate out of the waste sludge prior to digestion is only use full if a specific problem is encountered such as a decrease reactive digester volume or need for a lower P-index. An increased mixing intensity might already solve the accumulation issue. Caution is needed since redirecting this quantity of phosphate that would otherwise disappear in the digester struvite-sink is not risk free. If the implemented struvite process does not retain this redirected portion of the phosphorus flow transferred as good as the digester does this will increase the overall P-load towards the waterline.
3. Deterioration of dewatering properties after converting towards Bio-P is a serious challenge and needs to be addressed to avoid increasing costs. The beneficial effects of struvite and excess Mg dosing have now a proven track record. Although caution is needed when claiming dry matter gain without taking into account the contribution of converted solutes into solid struvite and correcting for the harvest fraction. The latter can only be correctly quantified when the portion of struvite already produced in the digester is taken into account. In addition, the effect of drying temperature when determining the dry matter content needs to be lowered to avoid under estimating the actual quantity of dewatered digestate to be hauled away at the end of the day. The proof will be in the eaten of the pudding.
4. Yellow is the new gold. Source separate urine treatment seems to be a very promising approach in extracting both N & P out of concentrated nutrient rich flow. Public perception will be important but within a generation a lot can be done.
To be continued.
Moerman Wim CTO NuReSys