Phosphorus Recovery from Wastewater: State of the Art Based Design, Sizing and Parametrization of a Crystallization Reactor

• Autor(a) principal: Branco, Clara Picareta
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/124291
• topic: Phosphorus; Wastewater; P-recovery; Struvite precipitation; Reactor; Solubility curve; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia do Ambiente

Phosphorous (P) is an essential element for all living organisms. There is no workaround or another element that can be substituted for it. Concurrently, phosphate rock is being increasingly consumed to produce P fertilizer to support global food production. Being a non-renewable and irreplaceable resource, phosphate rock depletion comprises P-scarcity and food security concerns. Potential geopolitical instability of countries producing phosphate also plays a major role in P-scarcity. While on the one hand, the responsible management of P helps grow the crops needed to feed a growing planet, on the other hand, excess P discharged into water bodies may cause eutrophication and water quality problems related with. Therefore, continuous efforts have been made to decrease P discharge by means of wastewater treatment techniques. Removing P from wastewater, especially through biological processes, may, however, carry associated problems in wastewater treatment plants (WWTP) as there is a potential for P resolubilization in their sludge handling system. P resolubilization results in P-rich internal streams and increases the P load to be treated. Hence, under favorable conditions, the P resolubilization may involuntarily precipitate struvite, which is usually responsible for clogging pipes and damaging the WWTP equipment. Interestingly, struvite crystallization is one of the most promising recovery techniques to mitigate or even solve the aforementioned problems in WWTP. Recovering P in the form of struvite, under controlled circumstances, not only prevents unintentional struvite formation and P load increase, as it also produces a slow release fertilizer with a market value. Furthermore, this P-recycling enhances the P-security and the P-loop closure. Against this background, one of the goals of this dissertation was the designing and sizing of a crystallization reactor that recovers P from wastewater in the form of struvite. Applying an existing methodology to obtain a struvite solubility limit curve, which is of paramount importance for the control parameters of the reactor, was another objective. Other aims were also to understand the fundamental principles of struvite crystallization and to review the struvite recovery technologies most commonly implemented worldwide at full-scale. The designing and sizing of a crystallization reactor was accomplished in this thesis and the rationale behind it was extensively described. To this end, the technologies review carried out was an invaluable support. As for the fundamental principles of struvite crystallization, they were described comprehensively here, and this allowed to understand the need of a solubility curve for the control parameters of the reactor. Accordingly, such a curve, referring to Chelas WWTP centrate, was determined: a 2nd order polynomial curve fitted the experimental data through an R2 of 0.96. Consequently, the applied methodology was proven to work with this centrate. Moreover, the application of this procedure allowed to make explicit some important aspects that happen to be not available in the literature. These aspects were also described here.