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Countercurrent stacked floc blanket reactor

Fall 2016

The presence of contaminants such as arsenic and fluoride in drinking water is a major health concern for rural communities around the world. Some of the most severe cases are in South-Asian countries such as India and Bangladesh, several regions in South America, and Africa. Arsenic and fluoride are natural occurring elements widely distributed throughout the environment and are highly toxic in their inorganic form. People in these parts of the world are exposed to elevated levels of inorganic arsenic through contaminated groundwater, which is often used for drinking, food preparation, and irrigation. Long-term exposure to these inorganics can lead to chronic poisoning, severe cases of which may lead to organ failure and internal hemorrhaging.

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Floc blankets have the potential to hold a large mass of PACl precipitate without generating high head loss and floc blankets can concentrate flocs in a floc hopper and thus eliminate the need for the wasteful process of backwashing. The disadvantage of floc blankets is that the fluidized bed is completely mixed over the residence time of the flocs. Thus flocs at the top of the floc blanket would include flocs that are in equilibrium with influent contaminant levels and thus the removal efficiency will be poor. To improve performance we propose to have countercurrent flow through 3 floc blankets with PACl injection and flocculation occurring at the influent to the 3rd floc blanket and the wasted flocs from the 3rd floc blanket being injected through a venturi (or other means) into the 2nd floc blanket. Similarly the wasted flocs from the 2nd floc blanket will be injected through a venturi into the first floc blanket. The wasted flocs from the first floc blanket will be in equilibrium with the influent contaminant and will be the waste stream from the treatment process.

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