Gaojie Li, Zhenjia Zhang
ABSTRACT: Psychrophilic anaerobic digestion recently has been demonstrated as a cost-effective option for the treatment of a range of wastewater categories. In this study. the treatment of alginate productionwastewaters was carried out in a pilot-scale expended granular sludge bed lEGSB) reactor. After a 40-day startup with two inocula. a 163-day experiment was run. from moderate to low temperatures, to treat seaweed-based-production wastewater. The results showed that inoculating with the active granular sludge instead of flocculent biomass can remarkably speed up the startup, and. at applied organicloading rates of 1.5 to 3.0 kg chemical oxygen demand (COD)/m3d, COD removal efficiencies of 55.4 to 72.69r were achieved. The volatile suspended solids ratio decreased slowly with operation time, as a result of the extremely slow growth rates of microorganisms and the accumulation of inorganic substances. Morphological examination and particle-size distribution of the granules revealed theirtendency to disintegrate. Inorganic precipitates, microorganism shift, and substrate limitations may have contributed to it. Water Environ. Res.. 82, 725 (2010).
KEYWORDS: anaerobic treatment, expended granular sludge bed reactor, alginate, low strength, ambient temperature.
School of Environmental Science and Technology. Shanghai Jiaotong University,Shanghai. P. R. China.
Alginate has widespread applications in the food and beverage, pharmaceutical, and bioengineering industries. Large quantities of water are used in the production process, especially when washing the raw seaweed and diluting the viscous initial alkaline extract to a viscosity suitable for filtration. Wastewater that is generated from filtration contains calcium from the calciumprecipitation and acid from the acid-conversion steps (McHugh. 2003). Some disposal methods for the solid wastes, the seaweed residue, and the used filter aid were found. There have been several positive studies reported on the use of this waste to adsorb heavy metals from industrial liquid wastes (Romero-Gonzalez et al.. 2003). Attempts to ferment this waste to produce ethanol from the cellulosecontent appear to be less promising, in economic terms (Horn et al.. 2000).
Alginate production wastewaters have a high content of carbohydrates, which makes them suitable for biological treatment. The presence of seaweed residue, cellulose, and colloidal suspended solids is responsible for the high chemical oxygen demand (COD) concentration and the turbid and brownish appearance of seaweedprocessing wastewater (SPW); on the other hand, the water used for washing and chemical reaction contribute to the large quantity of effluent. However, currently, because water supplies are limited, excess-calcium wastewater (ECW) is partially internally reused as a washing supply. Though recycling lowers the quantity and cost of water used by the factory , large quantities of salts (mainly calciumchloride) have to pass through the biochemical treatment stage. In addition, because seaweed residue is processed mostly to produce feed additives, the specific wastewaters that need to be treated mainly include seaweed washing wastewater (SWW), ECW. mannitol production wastewater (MPW). and remaining SPW, which have characteristics of large quantities and low strength.
Anaerobic digestion has beenused for over a century as a proven option for the effective treatment of a variety of wastewater from the food and beverage, agricultural, and chemicals sectors (McHugh et al.. 2003). The application of this natural methanogenic process is particularly attractive for the treatment of wastewaters in developing countries because of its favorable cost balance, energy production, lower sludge...