REVIEW - Recent developments in biological nutrient removal

Abstract

Biological nitrogen (N) and phosphorus (P) removal from municipal wastewater with the activated sludge (AS) system has been the preferred technology for the last 40 years. While several questions remain to be answered for more consistent, reliable and stable performance for enhanced biological P removal (EBPR), recent developments in this technology have focused on (i) increasing capacity and reducing the plant space footprint and (ii) improving N removal. To increase capacity and reduce AS system space, (a) integrated fixed-film activated sludge (IFAS), (b) external nitrification, (c) membrane, (d) aerobic granulation BNR systems and (e) more efficient N removal bioprocesses (anammox and nitrite shunt) have been developed. With IFAS, fixed media are added to the aerobic activated sludge reactor to make nitrification independent of the suspended AS sludge age. With external nitrification, nitrification is achieved in a side-stream fixed media reactor, which removes the size-defining nitrification process from the suspended AS system and halves its sludge age, improves sludge settleability and increases capacity. With membranes, secondary settling tanks are replaced with in-reactor membranes for solid-liquid separation. With aerobic granulation, the activated sludge process is controlled to form fastsettling granules comprising heterotrophs, nitrifiers, denitrifiers and phosphorus-accumulating organisms (PAOs) in a sequencing batch (SBR) type reactor -the granules not only settle fast but the SBR-type operation also removes the need for secondary settling tanks allowing higher reactor solids concentrations and hence smaller reactors. To achieve N removal more efficiently, methods are being developed to (i) short-circuit nitrification-denitrification (ND) by preventing nitrate formation and enforcing ND over nitrite -this requires less oxygen and organics than ND over nitrate allowing lower N concentrations to be achieved for the same influent organics concentration and oxygen supply, and (ii) encouraging the growth of anammox bacteria in the activated sludge which remove N autotrophically by combining ammonia and nitrite to form nitrogen gas -this halves oxygen demand for nitrification and requires no organics. These recent developments in BNR technology are briefly reviewed in this paper.

Resource recovery from and management of wastewater in rural South Africa: Possibilities and practices

“…The steady state mass balanced model was extended to include the growth of annamox bacteria in the N removal process. With the use of this model to predict the system performance, it was discovered that, if all the N removal takes place over nitrite instead (Ekama, 2015 ) Model used was an extended PWSSM model of Ekama (2009) to include the of over nitrate, oxygen saving would be 25% and the methanol savings would be 40%. These considerable savings encourage further research to reduce the growth of NOB and increase the growth of anammox bacteria in N-removal activated sludge systems.…”

Minimizing membrane bioreactor environmental footprint by multiple objective optimization

“…The energy demand eD (kWh) is calculated as: [7] where Pw, Peff and Ps represent the energy consumption for the air blowers, permeate extraction and the recycle pumps, respectively. Pw and Peff have been calculated according to literature ( is a constant for air, e is the blower efficiency (common range 0.7-0.9).…”

Endocrine Disrupting Compounds Removal Methods from Wastewater in the United Kingdom: A Review

“…In European activated sludge systems, the HRT is between four and fourteen hours [32] and this method provided better results than trickling filters. Several scientists have noticed that EDC removal with increased SRT is more efficient [42,[53][54][55][56][57]. While microfiltration membranes on their own would not support an efficient removal of EDC, it was proposed that EDC adsorption of particulate matter, that is preserved by the membrane, would condense EDC intensity in the effluent.…”