Effect of Calcium Oxide Dose on Thermal Reactions, Lime Speciation, and Physical Properties of Alkaline Stabilized Biosolids

• Published in: Water environment research 1998-03, Vol.70 (2), p.224-230
• Main Authors: Smith, Karen A., Goins, Lori E., Logan, Terry J.
• Format: Article
• Language: English
• Subjects: Acid soils; Agrology; Agronomy. Soil science and plant productions; Applied sciences; Biological and medical sciences; BIOSOLIDS; Calcareous soils; Evaporation; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Heat; LIMING; Liquids; Orchard soils; Other industrial wastes. Sewage sludge; Other nutrients. Amendments. Solid and liquid wastes. Sludges and slurries; PASTEURIZATION; Pollution; Research Papers; Sewage sludge; SOIL; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Speciation; Wastes
• ISSN: 1061-4303; 1554-7531
• DOI: 10.2175/106143098X127071

Quicklime (CaO) was added to a single sample of dewatered biosolids at rates of 5, 15, 20, 25, 30, 40, and 50% by weight (based on wet weight of the dewatered biosolids) in the laboratory. Temperature rise and water loss were monitored to determine caloric energy expended in heating and evaporation, and these values were compared to heat generation. The limed biosolids were analyzed by x-ray diffraction and thermal gravimetric analysis to determine the lime species present, and the pH rise when added to selected soils. Effects of lime dose on biosolids physical properties were examined by measuring selected physical characteristics of the limed products. Addition of CaO to dewatered biosolids produces heat through the exothermic conversion of CaO to hydrated lime$[{\rm Ca}({\rm OH})_{2}]$, with only small amounts of heat produced from the exothermic reaction of carbon dioxide$({\rm CO}_{2})$with${\rm Ca}({\rm OH})_{2}$to form calcium carbonate$({\rm CaCO}_{3})$. All heat produced was dissipated during heating of the biosolids and evaporation of water. Because of the predominance of${\rm Ca}({\rm OH})_{2}$in the limed biosolids, care should be taken in using these materials as liming agents and soil amendments because of the very high initial soil pHs (greater than pH 12) that can persist for weeks or more. Increasing lime dose improved the density and water-holding capacity of biosolids and improved their physical consistency.