The influence of organic matter load and pH correction reagents on the biochemical activity, composition and properties of anaerobic granular sludge during milk processing wastewater treatment has been considered. The process was modeled in laboratory bioreactors at 30 °C in a semi-continuous mode with model wastewater feed. Sodium bicarbonate, ammonium hydroxide and sodium hydroxide have been used as pH adjustment reagents. The main technological characteristics of the laboratory bioreactors were determined: rate of organic pollutant utilization, efficiency of wastewater treatment, pH of bioreactors liquid, and the proportion of debris in total mass of granules. It was shown that the type of pH correction reagent does not affect the organic matter utilization rate. The highest efficiency of model wastewater treatment (83-88%) and the closest pH to the optimum for methanogenic bacteria (6.9-7.2) was achieved while pH adjusted with sodium bicarbonate. The highest degree of granule destruction has been observed when sodium hydroxide was used to correct pH. The type of pH correction reagent affects the composition of the mineral part of the sludge and causes an increasing of the introduced cation proportion. Sodium bicarbonate has been recognized as preferable for pH correction in anaerobic bioreactors. The use of ammonia and sodium hydroxide solutions can be recommended for medium- and high-load systems. It has been experimentally established that sodium bicarbonate provides the most stable conditions for methanogenesis, maintaining pH depending on the organic load. Unlike hydroxide reagents, it does not cause significant disturbances in the granular structure, which is confirmed by microscopic studies and analysis of the mineral composition. At the same time, the use of sodium hydroxide leads to an increase in the proportion of fine particles in the reactor to 84% at high loads, which can negatively affect the efficiency of purification. The data obtained are important for optimizing the operation of industrial anaerobic reactors, especially when treating wastewater with variable composition and inclusions. Results of a study of the efficiency of buffer systems based on bicarbonates against strong alkalis to maintain stable operation of biological purification systems.

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