Mechanistic assessment reveals the significance of HRT and MLSS concentration in balancing carbon diversion and removal in the A-stage process

The efficiency of biodegradation processes for removal of tetracycline antibacterial drugs using activated sludge and river water inocula

Purpose

Tetracycline, chlortetracycline, and oxytetracycline are commonly prescribed antibiotics. Their extensive use results in a large stream of tetracyclines entering wastewater treatment plants (WWTPs). However, they can still be found in surface waters, which may suggest their incomplete removal in the WWTPs. The study was designed to show (i) how much of tetracyclines may be removed before they enter the environment, (ii) how tetracyclines may be removed after they enter surface water, (iii) how the presence of tetracyclines influence the metabolic activity of bacteria.

Method

Degradation of tetracyclines was studied using two types of inoculum, simulating degradation in WWTPs and rivers. Cell metabolic activity was assessed to show potential risks arising from their appearance in water.

Results

Complete primary degradation in the test with wastewater sludge inoculum was achieved within not more than 14 days. In the test with river water inoculum removal of both tetracycline and oxytetracycline did not exceed 20% in 28 days. Chlortetracycline was transformed rapidly but without considerable structural change. Although no considerable removal was achieved, bacterial activity in the river water test after 28 days was 10 times greater than while starting the test.

Conclusions

The study shows that appropriate retention of sewage in WWTPs must be provided. Otherwise, tetracyclines will accumulate in the environment, where their removal is limited, even though bacterial activity is still relatively high.

Metabolomic reveals the responses of sludge properties and microbial communities to high nitrite stress in denitrifying phosphorus removal systems

Nitrite, as an electron acceptor, plays a good role in denitrifying phosphorus removal (DPR); however, high nitrite concentration has adverse affects on sludge performance. We investigated the precise mechanisms of responses of sludge to high nitrite stress, including surface characteristics, intracellular and extracellular components, microbial and metabolic responses. When the nitrite stress reached 90 mg/L, the sludge settling performance was improved, but the activated sludge was aging. FTIR and XPS analysis revealed a significant increase in the hydrophobicity of the sludge, resulting in improve settling performance. However, the intracellular carbon sources synthesis was inhibited. In addition, the components in the tightly bound extracellular polymeric substances (TB-EPS) of sludge were significantly reduced and indicated the disturb of metabolism. Notably, Exiguobacterium emerged as a new genus when face high nitrite stress that could maintaining survival in hostile environments. Moreover, metabolomic analysis demonstrated strong biological response to nitrite stress further supported above results that include the inhibited of carbohydrate and amino acid metabolism. More importantly, some lipids (PS, PA, LysoPA, LysoPC and LysoPE) were significantly upregulated that related enhanced membrane lipid remodeling. The comprehensive analyses provide novel insights into the high nitrite stress responses mechanisms in activated sludge systems.