Digester volatile acids concentration

At this stage of development the model is restricted to a constant pH reactor and considers only two (pH and volatile acids concentration) of the five variables considered important for monitoring digester operation. This restriction of constant pH can be removed and the model extended to incorporate the interaction with bicarbonate alkalinity by considering the carbon dioxide-bicarbonate equilibrium as shown in Equations 16 and 17. 

Representative data from Run 1. which did not achieve steady state, as previously mentioned, are shown in Table V. This represents the baseline run without added nutrients. It was found that to maintain pH in the 6.8-7.2 range, 72 meq NaOH// of feed slurry was required this raised the sodium ion concentration in the digester to about 1670 mg//. Overall, the results of Run I were poor. The methane yield, volatile solids reduction, and energy recovery efficiency as methane in the product gas were low, and the volatile acids concentration in the digester effluent was high. 

The performance of Run 1 and the compositional data indicating possible nutritional deficiencies led to the evaluation of Runs 2, 3, and 4 at the same operating conditions as Run 1 except that the mixed nutrient solution in Table IV was added to the feed slurry to raise the concentrations of the nutrients. Sufficient nutrient formulation was added to reduce the C/N ratios of Runs 2, 3, and 4 to 16.3, 12.3, and 8.3, respectively. Substantial improvements were observed in the performance of these runs, but the volatile acids concentrations in the digester effluents were still high. Also, there did not seem to be a correlation between gas production and the concentration of added mixed nutrient solution. 

Run 7 exhibited the best methane yield of 3.51 SCF/lb VS added and the highest volatile solids reduction and energy recovery efficiencies of Runs 1 to 7. Also, the volatile acids concentration in the digester effluent is in the range... 

It should be pointed out that the performance of the packed-bed methane digester is more dependent perhaps on the influent volatile acids concentration than the overall VS loading rate. Thus, filter performance with acid-digester filtrate might be expected to be better than that obtained with methane-digester effluents having comparable volatile acids content. 

Smith [117] discussed the determination of tin in water. In the determination of low concentrations of the order of 40 ng of trialkyltin chlorides in sea water it has been observed that these compounds are very volatile and are easily lost upon evaporation with acid. Quantitative recovery of tin is, however, obtained in the absence of chloride ion during evaporation with acid. Preliminary removal of chlorides from sea water by passage down a column of IRA 400 resin before digestion with acid completely overcame loss of tin on subsequent evaporation, with acid giving a tin recovery of 90%. 

The studies of McCarty and co-workers have shown clearly that volatile acids are not toxic to methane bacteria at concentrations that would occur in stuck or sour digesters. On the contrary, evidence has been elucidated which indicates propionate retards the acid formers. Thus, the use of alkaline substances to maintain an adequate buffer capacity in an anaerobic waste treatment unit is a valid procedure. A word of caution is necessary pH control is not a universal palliative. Its only advantage is to prevent a bad situation from getting out of hand. The basic cause of the digester biochemical imbalance must be discovered and rectified. Unless this is done, pH control is worthless in the long run. In addition, care must be exercised in selecting an alkaline material that will not produce a toxic reaction. 

Reilly, P., O Doherty, J. V., Pierce, K. M., Callan, J. J., O Sullivan, J. T., and Sweeney, T. (2008). The effects of seaweed extract inclusion on gut morphology, selected intestinal microbiota, nutrient digestibility, volatile fatty acid concentrations and the immune status of... 

Opa.nte. There are two methods used at various plants in Russia for loparite concentrate processing (12). The chlorination technique is carried out using gaseous chlorine at 800°C in the presence of carbon. The volatile chlorides are then separated from the calcium—sodium—rare-earth fused chloride, and the resultant cake dissolved in water. Alternatively, sulfuric acid digestion may be carried out using 85% sulfuric acid at 150—200°C in the presence of ammonium sulfate. The ensuing product is leached with water, while the double sulfates of the rare earths remain in the residue. The titanium, tantalum, and niobium sulfates transfer into the solution. The residue is converted to rare-earth carbonate, and then dissolved into nitric acid. 

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