Dewatering waste-activated sludge using dissolved gas-flotation followed by filtration
After the successes of flotation of waste-activated sludge (WAS), using the new technique utilizing CO 2 gas as well as using model gas (80% N 2 +20% CO 2 ) in previous research because of the high water solubility of CO 2 gas, the aim of this study is to develop a simple method for dewatering WAS for easier reuse and safe disposal. The paper introduces a laboratory model for dewatering WAS in two stages: flotation followed by filtration. The first stage enables recycling a mixture of greenhouse gases containing 20% of CO 2 and 80% of N 2 gases by volume. The second stage uses a simple compression cell for dewatering WAS. Experiments were carried out to reduce the moisture content and volume of WAS. This was executed using compression force introduced by a low value of air pressure. Using the experimental dewatering model, promising results were obtained. Furthermore, other data were obtained, such as the effect of temperature on the efficiency of dewaterability. It is hoped that the results of this study will lead to further study of collecting industrial CO 2 gas emissions from burning fossil fuels for use in wastewater treatment to decrease the resulting harmful effects of global warming.
Floatation of Activated Sludge by Nascent Prepared Carbon Dioxide (Dept. C (Public))
Sludge treatment plays an important role in the treatment of wastewater. The production of sludge from wastewater treatment by the activated sludge method is relatively high, which causes problems in the treatment and disposal processes. The main purpose of sludge treatment is to reduce its water content, in addition to the prevention of pollution of the environment; one method of the activated sludge treatment methods is "Thickening by Floatation", which could reduce the water content of the sludge, facilitating the disposal process. In the present study, the floatation method is used to increase the sludge solid content by bubbles of carbon dioxide, which is directly prepared from sodium bicarbonate and hydrochloric acid, without the use of pressurized CO2, which results in the floatation of activated sludge solid particles. A floatation cell, composed of a glass column with a square base (13.5 x 13.5 cm) and height (50 cm), is used. The quantity of sodium bicarbonate ranged from 5 to 6.5 g/L; and that of the hydrochloric acid (10% concentration) ranged from 10 to 13 mL/L. The efficiency of this system was discussed with varying parameters, such as chemicals addition and initial solid content of sludge. The floatation cell showed a good result, regarding the increasing of the thickened sludge by floatation, from (0.6-1.1) % of solid content to (3.25-4.75) %; in addition, the current study has also shown better results, compared to the conventional pressurized CO2 cell.
FUNDAMENTAL STUDY OF BUBBLE FORMATION IN DISSOLVED AIR PRESSURE FLOTATION
This paper deals with the hydrodynamic performance of very fine gas bubbles required for dissolved air pressure flotation, which are produced by dissolving air in water under pressure and subsequent flashing to normal pressure. Experiments were carried out on generated air flow rate and bubble diameter when air was dissolved in water under 1-5 Kg/cm2 gauge and flashed to normal pressure through a nozzle. The results clarify the effects of dissolved pressure, liquid flow rate and nozzle geometry, and the empirical equations for the number of generated bubbles are obtained. Also, some theoretical considerations on the generated air flow rate and diameter of generated bubbles are discussed.