Vivianite & struvite: growing challenges for bioresources & wastewater operations
Smyth, M., Aqua Enviro, UK
(Free)
Vivianite is composed of iron, phosphorus, hydrogen and oxygen; all naturally present in wastewater. Levels of iron present are and will continue to increase for sites employing ferric dosing; whilst a site employing EBPR and anaerobic digestion will have greater levels of ortho-phosphate in liquors. Struvite causes similar challenges to vivianite with reduced capacity and labour- intensive cleaning resulting. One struvite control method is the dosing of iron, therefore the potential of the two to precipitate are often linked. Both enjoy some similarities in the conditions where they form and depending upon those conditions will appear as a scale/deposit in the feed to a digester, the digester itself or in pipework pre & post dewatering. Elevated phosphate levels will also reduce sludge dewaterability; along with vivianite a hidden cost of phosphorus removal.
This paper looks at the factors influencing deposition; how to assess the struvite/vivianite potential for your site; impact on thickening/dewatering and mitigation options.