Simultaneous nitrogen and phosphorus removal under low dissolved oxygen conditions

A full-scale test was operated by using low dissolved oxygen activated sludge process to enhance biological nitrogen and phosphorus removal. When the influent concentrations of CODCr, TN and TP varied in a range of 352.9 mg/L-1338.2 mg/L, 34.4 mg/L-96.3 mg/L, and 2.21 mg/L-24.0 mg/L, the average removal efficiencies were 94.9%, 86.7% and 93.0%, respectively. During the test period of two months, effluent meas of CODCr,, BOD5, NH3-N, TN and TP were below 50 mg/L, 25 mg/L, 10 mg/L and 1.0 mg/L respectively. The low dissolved oxygen activated sludge process has a simple flow sheet, fewer facilities and high N and P removal efficiency. It is very convenient to retrofit the conventional activated sludge process with the above process.

Seasonal and spatial variations in rare earth elements and yttrium of dissolved load in the middle,lower reaches and estuary of the Minjiang River,southeastern China

A bstract With the aim of elucidating the spatial and seasonal behaviors of rare earth elements(REEs), we investigated the dissolved REE concentrations of surface water collected during four seasons from middle, lower reaches and estuary of the Minjiang River, southeastern China. The results display that the REE abundances in Minjiang River, ranging from 3.3–785.9 ng/L, were higher than those of many of the major global rivers. The total REE concentrations(∑REE) were seasonally variable, averaging in 5 937.30, 863.79, 825.65 and 1 065.75 ng/L during second highest flow(SHF), normal flow(NF), low flow(LF) and high flow(HF) season, respectively. The R_(( L/M)) and R_((H/M)) ratios reveal the spatial and temporal variations of REE patterns, and particularly vary apparently in the maximum turbidity zone and estuary. REE patterns of dissolved loads are characterized by progressing weaker LREEs-enrichment and stronger HREEsenrichment downstream from middle reaches to estuary during all four seasons. Comparing with NF and LF seasons, in which REE patterns are relatively flat, samples of SHF season have more LREE-enriched and HREE-depleted patterns that close to parent rocks, while samples of HF season are more LREEs-depleted and HREE-enriched. REE fractionations from the middle to lower reaches are stronger in the SHF and HF seasons than those in NF and LF seasons. Generally, spatial and seasonal variations in REE abundance and pattern are presumably due to several factors, such as chemical weathering, mixture with rainfall and groundwater, estuarine mixing, runoff, biological production and mountain river characters, such as strong hydrodynamic forces and steep slopes. The highest Gd/Gd* always occurs at north ports during all four seasons, where most of the large hospitals are located. This suggests Gd anomalies are depended on the density of modern medical facilities. Y/Ho ratios fl uctuate and positively correlate to salinity in estuary, probably because of the geochemical behavior differences between Y and Ho.

Selective elimination of chromophoric and fluorescent dissolved organic matter in a full-scale municipal wastewater treatment plant

Effluent organic matter（Ef OM） from municipal wastewater treatment plants potentially has a detrimental effect on both aquatic organisms and humans.This study evaluated the removal and transformation of chromophoric dissolved organic matter（CDOM） and fluorescent dissolved organic matter（FDOM） in a full-scale wastewater treatment plant under different seasons.The results showed that bio-treatment was found to be more efficient in removing bulk DOM（in term of dissolved organic carbon,DOC） than CDOM and FDOM,which was contrary to the disinfection process.CDOM and FDOM were selectively removed at various stages during the treatment.Typically,the low molecular weight fractions of CDOM and protein-like FDOM were more efficiently removed during bio-treatment process,whereas the humic-like FDOM exhibited comparable decreases in both bio-treatment and disinfection processes.Overall,the performance of the WWTP was weak in terms of CDOM and FDOM removal,resulting in enrichment of CDOM and FDOM in effluent.Moreover,the total removal of the bulk DOM（P 〈 0.05） and the protein-like FDOM（P 〈 0.05） displayed a significant seasonal variation,with higher removal efficiencies in summer,whereas removal of CDOM and the humic-like FDOM showed little differences between summer and winter.In all,the results provide useful information for understanding the fate and transformation of DOM,illustrating that sub-fractions of DOM could be selectively removed depending on treatment processes and seasonality.

Bioavailability of wastewater derived dissolved organic nitrogen to green microalgae Selenastrum capricornutum,Chlamydomonas reinhardtii,and Chlorella vulgaris with/without presence of bacteria

Effluent dissolved organic nitrogen（DON） is problematic in nutrient sensitive surface waters and needs to be reduced to meet demanding total dissolved nitrogen discharge limits.Bioavailable DON（ABDON） is a portion of DON utilized by algae or algae ＋ bacteria,while biodegradable DON（BDON） is a portion of DON decomposable by bacteria.ABDON and BDON in a two-stage trickling filter（TF） wastewater treatment plant was evaluated using three different microalgal species,Selenastrum capricornutum,Chlamydomonas reinhardtii and Chlorella vulgaris and mixed cultured bacteria.Results showed that up to80% of DON was bioavailable to algae or algae ＋ bacteria inoculum while up to 60% of DON was biodegradable in all the samples.Results showed that C.reinhardtii and C.vulgaris can be used as a test species the same as S.capricornutum since there were no significant differences among these three algae species based on their ability to remove nitrogen species.

Spatial and temporal variations of two cyanobacteria in the mesotrophic Miyun reservoir, China

Spatial variations in phytoplankton community within a large mesotrophic reservoir （Miyun reservoir, North China） were investigated in relation to variations in physico-chemical properties, nutrient concentrations, temperature and light conditions over a 5 month period in 2009. The dynamics of phytoplankton community was represented by the dominance of cyanobacteria through summer and fall, following with a short term dominance of chlorophyta in late fall, and a relatively high abundance of diatom in October; on the other hand, maximum phytoplankton biomass was recorded in the north shallow region of Miyun reservoir with a higher nutrients level. Particular attention was paid to the impacts of environmental conditions on the growth of two cyanobacteria genera, the toxin-producing Microcystis and the taste ＆ odor-producing Oscillatoria. Microcystis biomass was in general greatly affected by water temperature and mixing depth/local water depth ratio in this reservoir, while the Oscillatoria biomass in the surface and middle layers was greatly affected by total dissolved phosphorus, and that in the bottom layer was related with the Secchi depth/local water depth ratio. Abundant Oscillatoria biomass was observed only in late September when Microcystis biomass decreased and allowed sufficient light go through.