Development Of New PH Titration Methods For The Determination Of Various Components In Anaerobic Digestion

Anaerobic digestion,which could degrade pollutants and generate hydrogen and methane simultaneously,is a favorable technique due to its advantage of high organic loading,less sludge,low cost and energy recycle.However,acidification,ammonia inhibiting and accumulation of phosphate would lead to the instability even failure of the anaerobic digestion.Therefore,methods of simpleness,rapidity and accuracy are crucial to monitor these factors.In this thesis,based on the charge balance,ionization equilibrium and mass balance in the solution,new pH titration methods were established to determine the concentration of VFA,ammonium,phosphate and bicarbonate in anaerobic digestion.Main contents and results of this thesis are as follows:1.A 2-point pH titration method was developed to determinate the concentration of VFA used hydrochloric acid as the titrant.The method was of high accuracy and precision when determined the concentration of acetic acid as a representative of VFA.The component of propionic acid and butyric acid would influence the titration accuracy owing to their different dissociation constants.When acetic acid coexisted with other buffer systems:The effect of bicarbonate on VFA titration was noticeable due to the loss of carbon dioxide during the titration.The disturbance of phosphate was expected to be weak.Ammonium and sulfide were of little effect on accuracy,however a small amount particles of elemental sulfur generated by oxidation during the titration would cause a decrease of precision slightly.The practical wastewater were test and the results showed that when the concentration of VFA exceed 3 mmol/L,the titration results were accurate enough.2.Three titration methods were developed according to the different pH ranges to determinate the concentration of ammonium in anaerobic digestion.The results showed that all of three methods were of high accuracy and precision to determine the concentration of ammonium.Phosphate buffer systems had slight influence on these methods,and the effect of VFAs was also insignificant.The impacts of both bicarbonate and sulfide could be exclude through sample acidification as well as dramatically stirring before titration,however the elemental sulfur generated during the acidification would cause a decrease of precision slightly.High ionic strength had a positive effect on the titration.Moreover,the methods also showed accurate results when evaluated with practical effluents.3.Five titration methods were developed according to the different pH range to determinate phosphate concentration in anaerobic digestion.The methods in the pH range of 1.65-2.65 and 11.82-12.82 were not suitable because of the siginificant errors caused by high concentration of hydrogen ion or hydroxide ion.Three titration methods were established in the pH range of 6.59-7.59 were all of high accuracy and precision for determining phosphate concentration.Ammonium buffer system was the main limiting factor to decrease the accuracy for all three methods,while VFA only had slight effect.The impacts of both bicarbonate and sulfide could be exclude through sample acidification as well as dramatically stirring before titration,however the elemental sulfur generated during the acidification would cause a decrease of precision slightly.In addition,ionic strength had an insignificant effect on the titration.4.Two titration methods were developed according to the different pH range to determinate carbonate concentration in anaerobic digestion.The results indicated that both methods were of high accuracy and precision.VFA had slight influence on both methods,while the effect of ammonium was significant especially on the first method.Both sulfide and phosphate buffer systems induced a certain error on two methods,and high ionic strength had a positive effect on the second method.