Evaluation of wastewater treatment’ efficacy: an ecotoxicological and ecological approach

• Autor(a) principal: Pinto, José Carlos Nereu
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/36298
• topic: Olive mill wastewater; Chemical precipitation technique; Circularity; Ecotoxicity; Waste reuse; Environmentally friendly solutions

Olive oil is a crucial part of Mediterranean cuisine, its consumption has only increased in the last ten years, and there is evidence that production will continue to grow accordingly. One of the olive oil’s more common byproducts: olive mill wastewater (OMWW), represents an undeniable hazard for both natural and human systems. Prolific in phytotoxic phenolic compounds and with generally high carbon content, OMWW’s complex chemical matrix represents a difficult challenge for wastewater treatment facilities and an even greater one for the environment. With the surcharge of an overcrowded planet with fewer resources, less space, and more people, it is evident that sustainable solutions that function outside the ordinary scale of a wasteful society are a requirement for the future existence of the natural world and humans themselves. The chemical precipitation technique (CPT) is hence proposed as an alternative to traditional wastewater management technologies, which are expensive, laborious, and protracted. CPT utilizes a single reagent – lime (Ca(OH)₂) – and a chemical reaction with atmospheric carbon dioxide (CO₂). This reaction will bring about immediate ion precipitation, resulting in a water matrix with a significant reduction of total nitrates, phosphorus, turbidity, and chemical oxygen demand (COD). As the resulting water matrix is considered “clean”, the resultant precipitate can be removed, repurposed, and employed elsewhere. Notwithstanding, some issues are important to consider before CPT’s usage as a wastewater treatment becomes integral for wastewater management. Not only must CPT alter the chemical composition of the most hazardous constituents to values under the legal threshold, but so should the ecological and toxicological outcomes be considered. Indeed, although quantitative legal thresholds represent the vast majority of legislative directives, ecotoxicological assays constitute a crucial part of wastewater management as they can demonstrate chemical, physical, and biological adverse qualitative reactions otherwise not perceptible nor knowable. Considering how ecologically important good wastewater management is, this work focused on a preliminary assessment of CPT’s ecotoxicological relevance for treating olive mill wastewater. For that, a battery of freshwater ecotoxicological assays with ecological relevant organisms was conducted: the microalgae Raphidocelis subcapitata, the crustacean Daphnia magna, the teleost Danio rerio, and the Oligochaete Lumbriculus variegatus were selected. Assays showed a significant decrease in toxicity for two tested organisms – D. magna and D. rerio – while only decreasing toxicity at low concentrations in R. subcapitata. In addition, L. variegatus showed no toxicity in either untreated or CPT-treated wastewater. These results, although still requiring complementation, demonstrate that post-CPT wastewater can be considered improved if not completely treated. Furthermore, future work and innovation in wastewater management can help and work in tandem with CPT, thus turning it into an intrinsic instrument for wastewater management to a highly circular, sustainable economy.