Treatment of fracturing wastewater by anaerobic granular sludge: The short-term effect of salinity and its mechanism.

The effects of salinity shock on the anaerobic treatment of fracturing wastewater regarding chemical oxygen demand (COD) removal performance, sludge characteristics and microbial community were investigated. Results showed COD removal efficiency decreased from 76.0% to 69.1%, 65.6%, 33.7% and 21.9% with the increase of salinity from 2.5 g/L to 10, 15, 25 and 45 g/L, respectively. The cumulative biogas production decreased by 13.8%-81.1% when salinity increased to 15-85 g/L. The increase of salinity led to the decline in particle size of granular sludge, and the activity of granular sludge, including SMA, coenzyme F420 and dehydrogenase, was inhibited significantly. Flow cytometry indicated the percentage of damaged cells in granular sludge gradually increased with the increase of salinity. Sequence analysis illustrated that microbial community structure in anaerobic digestion reactor was influenced by the salinity, high salinity reduced the diversity of archaea and decreased the abundance of methanogens, especially Methanosaeta.

Use of extracellular polymeric substances as natural redox mediators to enhance denitrification performance by accelerating electron transfer and carbon source metabolism.

Extracellular polymeric substances (EPS) extracted from waste activated sludge were used as endogenous redox mediator to enhance denitrification performance. The nitrate reduction rate increased 1.42-fold when EPS were added at 75 mg C/L (C represents total organic carbon). EPS addition decreased the charge transfer resistance and improved the electron transport system activity. The nitrate reductase and nitrite reductase activities improved by 29.7% and 25.4%, respectively. The activation energy of the system with EPS addition (25.82 kJ/mol) was 31.1% lower than that of the control group (37.49 kJ/mol). Besides, EPS could be used as electron carriers to accelerate electron transport; its primary role was similar to that of the quinone loop in the electron transfer chain. More importantly, EPS addition enhanced carbon source metabolism, which increased the available nicotinamide adenine dinucleotide yield to 1.21 times that of the control group, and thus promoted the denitrification performance of activated sludge.

Enhanced total nitrogen removal performance in a full scale Orbal oxidation ditch by a novel step aeration mode.

Two aeration modes, namely point aeration and step aeration, were proposed and implemented in a full scale Orbal oxidation ditch, and nitrogen removal performance was studied. The results showed that nitrogen removal performance under point aeration mode depended on oxygen supply control. Highest total nitrogen (TN) removal efficiency of 73.2% was achieved when oxygen input in the outer, middle and inner channel accounted for 50, 25 and 25% of total oxygen supply, respectively. With the same oxygen supply, both aeration modes demonstrated complete nitrification with over 97% ammonia nitrogen removal efficiencies. However, TN removal efficiency was 78.8% under step aeration mode, which was higher than that under point aeration. The pyrosequencing results indicated that microbial community composition was affected by aeration modes and step aeration mode was beneficial to the enrichment of denitrifiers. The greater diversity and relative abundance of denitrifiers enhanced TN removal under step aeration mode.