Inadvertently enriched cyanobacteria prompted bacterial phosphorus uptake without aeration in a conventional anaerobic/oxic reactor.

The enhanced biological phosphorus removal (EBPR) process requires alternate anaerobic and aerobic conditions, which are regulated respectively by aeration off and on. Recently, in an ordinary EBPR reactor, an abnormal orthophosphate concentration (PO43--P) decline in the anaerobic stage (namely non-aerated phosphorus uptake) aroused attention. It was not occasionally but occurred in each cycle and lasted for 101 d and shared about 16.63 % in the total P uptake amount. After excluding bio-mineralization and surface re-aeration, indoor light conditions (180 to 260 lx) inducing non-aerated P uptake were confirmed. High-throughput sequencing analysis revealed that cyanobacteria could produce oxygen via photosynthesis and were inhabited inside wall biofilm. The cyanobacteria (Pantalinema and Leptolyngbya ANT.L52.2) were incubated in a feeding transparent silicone hose, entered the reactor along with influent, and outcompeted Chlorophyta, which existed in the inoculum. Eventually, this work deciphered the reason for non-aerated phosphorus uptake and indicated its potential application in reducing CO2 emissions and energy consumption via the cooperation of microalgal-bacterial and biofilm-sludge.

Elucidating performance failure in the use of an Anaerobic-Oxic-Anoxic (AOA) plug-flow system for biological nutrient removal.

The Anaerobic-oxic-anoxic (AOA) process is a carbon-saving and high-efficiency way to treat municipal wastewater and gets more attention. Recent reports suggest that in the AOA process, well-performed endogenous denitrification (ED), conducted by glycogen accumulating organisms (GAOs), is crucial to advanced nutrient removal. However, the consensuses about starting up and optimizing AOA, and in-situ enriching GAOs, are still lacking. Hence, this study tried to verify whether AOA could be established in an ongoing anaerobic-oxic (AO) system. For this aim, a lab-scale plug-flow reactor (working volume of 40 L) previously operated under AO mode for 150 days, during that 97.87 % of ammonium was oxidized to nitrate and 44.4 % of orthophosphate was absorbed. Contrary to expectations, under AOA mode, little nitrate reduction (only 6.3 mg/L within 5.33 h) indicated the failure of ED. According to high-throughput sequencing analysis, GAOs (Candidatus_Competibacter and Defluviicoccus) were enriched within the AO period (14.27 % and 3 %) and then still dominated during the AOA period (13.9 % and 10.07 %) but contributed little to ED. Although apparent alternate orthophosphate variations existed in this reactor, no typical phosphorus accumulating organisms were abundant (< 2 %). More than that, within the long-term AOA operation (109 days), the nitrification weakened (merely 40.11 % of ammonium been oxidized) since the dual effects of low dissolved oxygen and long unaerated duration. This work reveals the necessity of developing practical strategies for starting and optimizing AOA, and then three aspects in future studying are pointed out.

Towards low carbon demand and highly efficient nutrient removal: Establishing denitrifying phosphorus removal in a biofilm-based system.

The combined denitrifying phosphorus removal (DPR) and Anammox process is expected to achieve advanced nutrient removal with low carbon consumption. However, exchanging ammonia/nitrate between them is one limitation. This study investigated the feasibility of conducting DPR in a biofilm reactor to solve that problem. After 46-day anaerobic/aerobic operation, high phosphorus removal efficiency (PRE, 83.15 %) was obtained in the activated sludge (AS) and biofilm co-existed system, in which the AS performed better. Phosphate-accumulating organisms might quickly adapt to the anoxic introduced nitrate, but the following aerobic stage ensured a low effluent orthophosphate (<1.03 mg/L). Because of waste sludge discharging and AS transforming to biofilm, the suspended solids dropped below 60 mg/L on Day 100, resulting in PRE decline (17.17 %) and effluent orthophosphate rise (4.23 mg/L). Metagenomes analysis revealed that Pseudomonas and Thiothrix had genes for denitrification and encoding Pit phosphate transporter, and Candidatus_Competibacter was necessary for biofilm formation.

Application of an integrated loach-plant-substrate-microbes non-aerated saturated vertical flow constructed wetlands: Mechanisms of pollutants removal and greenhouse gases reduction.

This study established an integrated loach-plant-substrate-microbes non-aerated saturated vertical flow constructed wetlands (VFCWs) to enhance pollutants removal efficiencies and reduce greenhouse gas emissions simultaneously. The results of the VFCWs experiment indicated that the removal efficiencies of chemical oxygen demand, total phosphorous, and total nitrogen in loach systems were significantly higher than those of non-loach systems, achieving 59.16%, 35.98%, and 40.96%, respectively. The CH4 and N2O emission fluxes were also significantly reduced in the integrated system, resulting in lower global warming potential (GWP) and GWP per unit of pollutants removal. Loaches promoted the transportation of oxygen, facilitated the re-contact and utilization of sediments, reduced CH4 emission, and enhanced nitrogen conversion and phosphorus accumulation. Increased bioavailable carbon and nitrate-nitrogen in the integrated system improved the abundance of denitrifying bacteria, which supported complete denitrification, reducing N2O emissions with high pollutant removal.

Quantitative comparison of clamworm (Perinereis aibuhitensis) and crab (Macrophthalmus japonicus) burrowing effects on nitrogen and phosphorus dynamics at the sediment-water interface.

Exploring nitrogen and phosphorus dynamics in estuarine ecosystems is of great significance for understanding the nutrient cycle in terrestrial and marine ecosystems. However, the ecological functions of common species remain unclear because there is a dearth of observational data. To quantitatively compare the bioturbation effects of the clamworm Perinereis aibuhitensis and crab Macrophthalmus japonicus on the migration of nitrogen and phosphorus in the sediment-pore water-overlying water interfaces, an indoor experiment was carried out using microcosms containing substrate, water, and living specimens collected from the Dagu Estuary, China. The physical structure of the sediments was greatly altered by both clamworms and crabs, and the amount of suspended particulate matter in the overlying water was in the order: crab > clamworm > control groups. Sediments, especially the 0-2 cm layer, were continuously mineralized under bioturbation, releasing NH3-N, NO2--N, NO3--N, and dissolved total phosphorus. During the experiment, the release rate of NH3-N (2.45 mg L-1 to 10.23 mg L-1), NO2--N (0.25 mg L-1 to 7.34 mg L-1), NO3--N (0.02 mg L-1 to 6.03 mg L-1), and dissolved total phosphorus (0.07 mg L-1 to 0.16 mg L-1) in the crab group was higher than that in the clamworm group (NH3-N, 0.93 mg L-1 to 6.11 mg L-1; NO2--N, 0.51 mg L-1 to 6.18 mg L-1; NO3--N, 0.01 mg L-1 to 5.24 mg L-1, and dissolved total P, 0.04 mg L-1 to 0.08 mg L-1). Our findings indicate that crabs might play a more important role in promoting nitrogen and phosphorus migration than clamworms because of their stronger bioturbation strategies in sediments. Bioturbation by both clamworms and crabs reduced nitrogen and phosphorus accumulation in surface sediments and accelerated organic matter mineralization in the sediments, which may promote nutrient recycling in estuarine ecosystems.