Continuous flow reactor with elevated wastewater pH was maintained at 12 hours HRT and 15/15 minutes aeration/nonaeration intervals. Values of pH were in the range of 8.0-8.5. Three rates of volume reactor filling by carriers were investigated: 60%, 40% and 20%.

The elevated pH caused the ammonia release and inhibition of the second phase of nitrification and this way the total nitrogen removal process was shorten by elimination of two elementary processes: nitratation and denitratation (figure 8).

The free ammonia concentration value, calculated accordingly to equation 6 was equal to appr. 1 mg N/dm3, what is known as a limiting value for inhibition of nitrification second phase [42]. The part of free ammonia could be released as the result of amino acids denaturization during alkalinity process, but due to relatively low concentration of organic nitrogen (mainly amino acids) in inlet wastewater (maximum 10% of total nitrogen) this factor can be neglected. In these conditions the SND process was achieved (shortened nitrogen removal process) what had been indicated by temporary nitrites accumulation. It is known and was stated by several authors [51] that as a result of ammonia inhibition of second phase of nitrification, mediate and final products are released simultaneously.

The higher removal efficiency was achieved at higher volume carriers filling of reactor (figure 9). The rise in pH value versus the rise of nitrogen compounds removal rate, what was observed by other authors [52].

The lime addition resulted in some changes in biomass, e. g. reducing organic fraction rate in biomass of 25% comparing to the process without lime addition. The lime in the liquid phase and on the carriers surface were some kind of "condensation centers" and caused the higher concentration of both biomass form. The smaller amount of carriers enabled more undisturbed carriers movement (figure 10). The lime addition caused also the less susceptibility of carriers pores for clogging by biomass.