Long term operation of a granular sequencing batch reactor at pilot scale treating a low-strength wastewater

Aerobic granular sludge is presented as an alternative technology to conventional activated sludge processes for the treatment of low-strength wastewaters. Results obtained with granular aerobic reactors at laboratory scale are promising but, there are few studies carried out at pilot scale. Therefore, more information about the stability of granules and their performance at larger scale is needed to establish if aerobic granulation could be a feasible treatment. With this aim, a 100L granular sequencing batch reactor (GSBR) operating at high loading rate and treating low-strength wastewater for simultaneous carbon, nitrogen and phosphorus removal was operated for 11months. Mature granules prevailed in the GSBR during a period of 5months (from days 150 to 330), with a SVI30 of 13±6mLg−1 TSS, a granule density around 114±5g TSS L−1 and an average particle size of 2.4mm. The biological nitrogen removal with mature granules was mainly performed via nitrite, probably due to the large granule size achieved. Nitrification efficiency was higher than 75% and occurred simultaneously with denitrification during the aerobic phase of the GSBR. A progressive accumulation of P-salts (probably apatite), was found from days 150 to 300, which could enhance the destabilization of granules at the end of the experimental period. ► A GSBR at pilot scale was stably operated during almost a year. ► The GSBR removed C, N and P from a low-strength wastewater at high loading rates. ► Long term operation with EBPR leads to the accumulation of inorganic particles in the granules. ► BNR was via nitrite, and simultaneous nitrification and denitrification was achieved.