Cyanobacterial bloom in Korea increased dramatically within last few years, due to the slow water flow as well as eutrophication generated throughout the rivers in Korea. Microcystis and Anabaena are known to be the main culprits affecting the aquatic environment in Korea at the moment. Cyanobacteria, especially in case of Microcystis, tend to form aggregates themselves. These aggregates float up to the surface of the water for photosynthesis during day and float down to the bottom during the night for respiration. Nocturnal behavior of these benthic cyanobacteria make it hard for researchers to resolve the cyanobacterial bloom. Several methods for preventing and removing algal bloom such as electro coagulation flotation (ECF) are now being implemented. ECF, in particular, has its advantage of utilizing the already floating cyanobacteria to form bigger yet stable aggregates for the removal process. Further utilization of cyanobacterial aggregates such as anaerobic digestion can also be implemented.
Sulfate Reducing Bacteria (SRB)
Biotechnological application of sulfate reduction mostly results from the need of removing sulfate containing wastewaters. Such process application intrinsically implies large production of odorous, corrosive gas known as sulfide. However, through the development and operation of a novel up-flow anaerobic sludge blanket (UASBr) based on sulfate-reducing bacteria for wastewater treatment, energy in wastewater, electricity, and high value added products can be obtained. In addition, treated water can be recovered and recycled. Not only can this approach solve the collective problems of current water treatment systems but can also lead to an integrated process towards providing and securing sustainable water development.
Shortage of Sites for Waste & Low Biodegradability
Wastewater treatment on the basis of activated sludge is a core technology when it comes to the removal of organic wastes, generates an enormous amount of sludge called waste activated sludge (WAS). It is of necessity to reduce the volume prior to disposal. Anaerobic digestion (AD) is a biological way of achieving it; what is better, it concomitantly produces biogas. AD has a good many advantages for the purpose of WAS treatment, such as lower operation energy consumption, legitimate performance and stabilization, but low biodegradability of large compounds, e.g., WAS, in the first hydrolysis step stands an issue.
Hydrodynamic Cavitation & High Methane Production Rate
High biodegradability, enhancing methane production, can be achieved by pre-treatment of sludge and many pretreatments such as thermal, physical and chemical treatment has been studied. Our group focus on hydrodynamic cavitation (HC) which is probably a physical means best suited for the sludge treatment; it needs much reduced energy consumption, easy scaling-up and efficient method.
Its principle is simple as follows. When a fluid passes through an orifice plate or a venturi tube, pressure drops can occur below vapor pressure and as a result, bubbles are generated. When the fluid pressure is restored at a distance from the throat, cavities collapse subsequently. This phenomenon causes increase of pressure (100-5,000 atm) and temperature (500-15,000 K), leading to form hydroxyl radicals because of hemolytic cleavage of the water molecules.
Struvite Precipitation & Ammonia Stripping
The AD process generally releases high levels of ammonia (NH4+) and phosphate (PO4 3-) which can generate algal bloom. Post-treatment is essential and byproduct-fertilizer can be recovered. In our group, HC apply to 1) recover NH4+ and PO4 3- with precipitation of struvite and 2) recover NH4+ with stripping & absorption.
1. Pre-treatment of WAS using HC to improve sludge volume reduction & methane production.
2. Post-treatment of Digestate using HC, recovering with ammonia & phosphate