Comparison of the results of orthophosphates removal from sewage using electrocoagulation method and metal digestion method

Celem niniejszych badań było porównanie efektów usuwania związków fosforu (ortofosforanów) z wód z dodatkiem ortofosforanów, z wykorzystaniem dwóch metod: metody elektrokoagulacji (z wykorzystaniem procesów elektrochemicznych z użyciem prądu stałego) i metody roztwarzania metali (z wykorzystaniem procesów korozyjnych).There is a search in progress for some efficient methods of removing biogenic compounds from the treated sewage. Unquestionably, effective methods of phosphorus compounds removal include precipitation methods. The most common is the chemical precipitation method based on applying iron, aluminium or calcium salt to the solution and electrocoagulation. These methods utilise low solubility of metal phosphates and their sorption on the surfaces of the forming agglomerates. The real mechanism is quite complicated and consists of transforming phosphorus compounds into insoluble forms, and then separating them from the sewage by flotation, sedimentation, filtration. The method of iron solution should also be accounted into similar physical and chemical methods. The main difference between the aforementioned methods lies in the way of applying the precipitation agent to the solution. The method of iron solution is based on similar premises as the electrocoagulation method, however, metal ions here are dissolved into the solution as a result of spontaneous corrosion processes and, due to the further transformations in the sewage environment, they are to be responsible for phosphorus removal. The article presents comparative tests on a laboratory scale. The electrocoagulation method and metal digestion method were compared with regard to the effectiveness of orthophosphates removal from synthetic sewage. The comparison of both methods suggests that they can bring similar results of removing phosphorus (ortophosphates) from sewage. The process of reduction of concentration of orthophosphates in sewage occurs faster when the electrocoagulation method is used. However, with a longer test duration, better results are achieved using the metal digestion method. It was also noted that both methods introduce different amounts of iron into the solution. The methods differ with regard to the amount of iron remaining in the sewage in a suspended form. This indicates a better use of iron ions in the metal digestion method and it slightly limits the problem of an excessive amount of sludge