Estudo da biodegrabilidade da matéria orgânica (DBO/DQO) nas àguas residuais em despejo ao longo da Marginal: Cidade de Quelimane, Zambezia - 2023

Abstract

Urban surface runoff is the main transport mechanism that introduces toxic substances into receiving waters (rivers, lakes and estuaries) causing numerous problems, including overloading sewage and rainwater treatment plants, also damaging the its functions. However, assessing the biodegradability of organic matter makes it possible to assess the type of treatment process suitable for wastewater. Therefore, the present study aims to evaluate the state of biodegradability of organic matter depending on the BOD and COD of wastewater discharged along the riverbank, Quelimane’s city, Zambezia. To this end, samples were collected in three sewage terminals on the Quelimane waterfront using plastic bottles at a depth of 30 cm and immediately after collection, pH, temperature, conductivity, TDS, salinity, dissolved liquid oxygen were determined by digital potentiometry. (LDO and LDO5) and turbidity. These were then taken to the chemistry laboratory of the School of Marine and Coastal Sciences (ESCMC) where 250 mL of the sample was incubated at 20oC for 5 days to determine BOD5. COD was determined through a relationship between the visibility of the Secchi disk and the chemical oxidation of organic matter established by equation 1. At all points in the CNTP, the maximum observed pH was 8.64 and the minimum was 8.02, the salinity ranged from 0.66 to 6.41 ppm, TDS ranged from 641 to 2160 mg/L, the greatest transparency was seen at point 2 with 40 cm and lowest at point 3 with 5 cm of visibility. The maximum LDO observed was 15.10 mg/L and minimum 10.0 mg/L and after 5 days this parameter varied from 11.10 mg/L to 18.60 mg/L. The highest 5-day BOD observed was 7.3 and a minimum of 0.1 mg/L and the COD ranged from 5.6 to 22.9 mg/L. The variation in BOD/COD was at all points, on average from 0.25 to 0.54 mg/L. It was found that there is a lot of already degraded matter and, through these values, it was concluded that the non-biodegradable fraction of matter present in this sewage is high, making it appropriate to apply physical-chemical processes and, after feasibility studies, biological processes for the treatment of these bodies of water before their discharge into the estuary. Therefore, it was appropriate to apply the following treatment techniques: sedimentation, flocculation and suspended biomass.