Controle da eutrofização e de florações de cianobactérias em corpos d agua salobras: avaliação da eficácia e aplicabilidade da combinação de coagulantes e adsorventes de fósforo em fase sólida

Abstract

The control upon eutrophication and cyanobacterial bloom can be achieved reducing the phosphourus (P) availability in the water. Eutrophication is considered the major problem on water quality world wide resulting in proliferation of harmful cyanobacterial blooms. Controling phosphorus is crucial to mitigate eutrophication and should focusing on both reduction of external and internal loading once phosphorus in the sediment can delay water quality recovery for decades. Jacarapaguá lagoon, once crandle for biodiversity and source of fishing resource, is highly eutrophicated due the lack of sewage treatments leading to intese cyanobacterial blooms. This thesys aims to evaluate the efficacy and applicability of the combination between coagulants and phosphate adsorbants on the control of eutrophication and cyanobacterial blooms in Jacarepaguá Lagoon. The monitoring during the period between nov/2014 and dez/2017 showed high mean concentrations of phosphorus (1,3±0,9 mg L-1) and total nitrogen (4,4±1,9 mg L-1). The phytoplankton was mainly composed by function group M in most part of the year and represented by Microcystis aeruginosa. The temperature was the main driver of this dominance observed in the Redundance analyse (RDA). In the coldest periods the increasing in salinity and water transparence facilitated the higher contribution of groups X1, J, F, X2, Y, C, MP and P. Experiments conducted in the lab evidenced: i) low doses (≤ 8mg Al L-1) of polyaluminium chloride (PAC) combined with ballast (Red soil, lagoon sediment or Lanthanum modified bentonite LMB) was efficient to remove cyanobacteria; ii) BML (400g m2) reduced significantly the phosphorus release from sediment in deonized water or lagoon water with and without cyanobacteria; iii) in sediment cores, PAC + LMB reduced the P flux from 9.9 (±3.3) to 4.6 (±0,3) mg P m-2 d-1 over the experimental period of 3 months. In summary, the water temperature was the main driver of M. aeruginosa bloom. Combining coagulante and ballast is a fast, cheap and safe curative techinique to mitigate harmful cyanobacterial bloom effects. The combination of LMB + PAC is a promissing techinique to diminish the internal P loading speeding up lagoon recovery once external loading is also reduced.