China
Africa
Explore chapters and articles related to this topic
Electroplating/Metal Finishing Wastewater Treatment: Practical Design Guidelines
Published in John M. Bell, Proceedings of the 43rd Industrial Waste Conference May 10, 11, 12, 1988, 1989
Richard D. Johannes, Gregory J. Humpal, Wayne V. Schmidt, Robert O. Hoffland
Sodium bisulfite and sodium metabisulfite are commercially the same and are treated as such in this discussion. Reduction of chrome using either one is widely used in place of SO2, especially in smaller systems. For small systems, where the flow generation rate is less than 20 gpm, batch chrome reactors, using either Na2S2O5 or NaSO3 are more attractive cost-wise. For these systems, the use of sodium salts is more efficient than SO2. While the reagents are about 4 times more expensive than SO2, their use eliminates use of gas cylinders. Either is supplied from a solution make-up tank by means of a chemical feed pump activated by an ORP controller. Acid demands will be higher with these sulfite derivatives because of their alkalinity. When added to water, they hydrolyze to create sulfurous acid (which is the real reducing agent) and sodium hydroxide. For each mole of salt added to the waste stream, one mole of NaOH is released. As the optimal pH for chromium reduction is in the range of 2–3 (same as SO2), they require a greater dosage of acid to maintain this pH.
Precombustion/Postcombustion Desulfurization
Published in S. Komar Kawatra, Advanced Coal Preparation and Beyond, 2020
In addition to lime and limestone, a number of other absorbents have been used to improve the efficiency of sulfur removal or to recover the sulfur in a marketable form while regenerating the absorbent. Next-generation scrubbers are therefore under development to improve the efficiency and reduce the quantity of unmarketable waste products (Feeney, 1995; Anonymous, 1992a,b). Several of the scrubber technologies that use other absorbents are as follows: Dual-alkali process: In this process, the absorption of sulfur dioxide is first carried out using a solution of a sodium alkali, such as NaOH, Na2CO3, or Na2SO3. Since these are all very soluble in water, they can absorb the sulfur dioxide very rapidly and completely and can be easily oxidized afterwards. Also, the absorbent is a clear liquid rather than a slurry, and so the problems with scaling and plugging of the scrubber are much reduced (Valencia, 1982). The oxidized sulfur-bearing alkali is then circulated to a vessel, where it is reacted with lime or limestone, which precipitates the sulfur as calcium sulfate and regenerates the sodium alkali. A flow diagram of the process is shown in Figure 3.3. The dual-alkali process is reported to be stable and resistant to disturbances, and to be capable of removing more than 99% of the sulfur dioxide from flue gases (Valencia, 1982; Hodges et al., 1992). Wellman-Lord process: This is a regenerable-sorbent process, producing SO2 gas, which can be sold for industrial uses. It uses a solution of sodium sulfite (Na2SO3), which absorbs SO2 and becomes a sodium bisulfite solution (NaHSO3). The sodium bisulfite is then decomposed in a forced circulation evaporator, releasing the SO2 at sufficiently high concentration to be compressed and sold as SO2 gas or used for producing elemental sulfur or sulfuric acid (Couch, 1995).Magnesium oxide process: The magnesium oxide slurry is used to collect SO2, and the resulting magnesium sulfite is thermally treated to release the SO2 and regenerate the absorbent, as shown in Figure 3.4. Like the Wellman–Lord process, this process is relatively complex and has a capital cost about 14% higher than limestone scrubbers (Burnett and Wells, 1982). It is therefore only economically viable when there is a reliable market for the by-products (Vernon and Jones, 1993).
Synthesis of natural starch from Elaeis guineensis trunk biomass applying bisulphite steeping method: Optimization by RSM
Published in Journal of the Air & Waste Management Association, 2022
Zaber Ahmed, Mohd Suffian Yusoff, Mokhtar Kamal N.H., Hamidi Abdul Aziz
After washing properly, 500 gm of freshly shredded and uniformly chipped OPT meal were steeped in sodium bisulfite (NaHSO3) solution at room temperature. The strength of bisulfite solution varied from 0.2% to 1% (w/v) (Madruga et al. 2014), while the variable steeping duration was 2 h to 10 h (Maniglia and Tapia-Blácido 2016) at a different mixing ratio (w/v) of 1:1, 1:1.5 and 1:2 (with the initial weight of OPT). The accumulation of sodium bisulfite solution crumbles the protein–starch matrices and restrains the growth of microorganisms (Sulaiman et al. 2013). Sodium bisulfite produces sulfur dioxide in the presence of water, which eventually inhibits microbial growth and anionic bisulfite ion (HSO3−) influence on breaking the starch–protein bond (Öztürk and Mutlu 2018). Once the steeping duration was over, the OPT meal was macerated with bisulfite solution homogenously in several batches (5 min each batch) using an industrial grinder, and the slurry was placed into a nylon screen for separation. After squeezing the slurry fairly, the filtrates were placed in a plastic dish. For extracting the residual starch, the remainder was passed through a similar procedure. The ultimate filtrates were screened through a 212 μm sieve and allowed for two-hour settlement. After the settlement period, the supernatant was removed by leaning the dish, and two liters of aquatic bisulfite solution was mixed thoroughly with the precipitate and allowed to settle again for two hours. Discarding the floated matter as before, the residue was mixed with UPW at a variable mixing ratio (w/v) (from 1:0.3 to 1:0.7 based on the initial weight of OPT), for washing out the soluble impurities from the starch.