Effects of Nitrate Concentration in Main Anoxic Zone on Denitrifying Dephosphatation

The effects of nitrate concentration in the main anoxic zone on denitrifying dephosphatation capability were conducted based on modified University of Cape Town （MUCT） process. Meanwhile the relation between optimal nitrate concentration （Nopt） and influent C/N ratio was evaluated, in which the influont chemical oxygen demand （COD） concentration was stabilized at （2905：10）mg/L, the influent total phosphorus （TP） concentration was stabilized at （7.0±0. 5）mg/L. The results indicated that： （1） the nitrate concentration in the main anoxic zone had an effect on denitrifying dephosphatation capability, and the average percentages of anoxic phosphorus uptake in total phosphorus uptake （ηa） increased with nitrate cancentration increasing, i.e., increasing from 62.1% at2.0 mg/L to63.7%, 65.6%, 68.1%, and 72.3% at 2.2, 2.4, 2.6 and 2.8mg/L, respectively; （2） the Nopt as function of influent C/N ratio could be calculated by the equation： y = 0.67x^2-7.79x ＋ 22. 21; the maximum percentages of anoxic phosphorus uptake in total phosphorus uptake （ηa,max） as function of the Nopt could be calculated by the equation： y=0.77-0.33e^-（x/1.52）. The Nopt was the important control parameter that must be optimized for operation of conveational biological nutrieat removal activated sludge （BNRAS） system.

Zoning of Nitrite and Nitrate Concentration in Groundwater Using Geografic Information System (GIS), Case Study: Drinking Water Wells in Yazd City

Studies have demonstrated that the presence of nitrate and nitrite in drinking water can cause some disease such as cancer and blu baby in the infant. The Environmental Protection Agency (EPA) has since adopted the 10 mg/L standard as the maximum contaminant level (MCL) for nitrate-nitrogen and 1 mg/L for nitrite-nitrogen for regulated public water systems. Given the importance of nitrate and nitrite in drinking water as well as GIS ability in spatial analysis of various factors in the groundwater, this study aimed to evaluate concentration of nitrate and nitrite in the drinking water wells of Yazd using two IDW (Inverse Distance Weighting) and Kriging models. In this descriptive study, the applied data on the water quality of underground water of Yazd Environmental Health Office and the average annual nitrate and nitrite in 2015 were related to 24 wells in the studied area. The nitrate and nitrite rate in groundwater in wells was compared to the standard amount of Institute of Standard and Industrial Researches and then was analyzed via Arc GIS software using IDW and Kriging interpolation methods. The mean concentration of nitrate was 17.62 ± 3.08 mg/l and for nitrite was 0.011 ± 0.003 mg/l in the wells. In the all studied zone, the nitrate and nitrite rate was in the standard range according to the National Standard of Iran (No. 1053). In this study, Kriging interpolation method was more efficient than IDW method.

Effect of nitrate concentration on filamentous bulking under low level of dissolved oxygen in an airlift inner circular anoxic-aerobic incorporate reactor

This laboratory research investigated a possible cause of filamentous bulking under low level of dissolved oxygen conditions （dissolved oxygen value in aerobic zone maintained between 0.6-0.8 mgO2 /L） in an airlift inner-circular anoxic-aerobic reactor. During the operating period, it was observed that low nitrate concentrations affected sludge volume index significantly. Unlike the existing hypothesis, the batch tests indicated that filamentous bacteria （mainly Thiothrix sp.） could store nitrate temporarily under carbon restricted conditions. When nitrate concentration was below 4 mg/L, low levels of carbon substrates and dissolved oxygen in the aerobic zone stimulated the nitrate-storing capacity of filaments. When filamentous bacteria riched in nitrate reached the anoxic zone, where they were exposed to high levels of carbon but limited nitrate, they underwent denitrification. However, when nonfilamentous bacteria were exposed to similar conditions, denitrification was restrained due to their intrinsic nitrate limitation. Hence, in order to avoid filamentous bulking, the nitrate concentration in the return sludge （from aerobic zone to the anoxic zone） should be above 4 mg/L, or alternatively, the nitrate load in the anoxic zone should be kept at levels above 2.7 mg NO-3N/g SS.

Influences of external nutrient conditions on the transcript levels of a nitrate transporter gene in Skeletonema costatum

To verify the feasibility of high-affinity nitrate transporter gene （Nrt2） as an indicator of nitrogen status, changes in the transcript levels of transcripts associated with phosphate starvation and different nitrate concentrations were studied using real-time quantitative reverse-transcription PCR （QRT-PCR） technology in batch cultures of Skeletonema costatum. The results show that compared with P-replete condition, P starvation could reduce the Nrt2 transcript levels apparently. Nrt2 transcript levels had a significant negative linear correlation with nitrate concentrations below 40 pmol/L. The results of 48 h short-term incubation experiment under different nitrate concentrations confirmed this correlation, and the following regression equation is built： y = -3.305x ＋ 98.95, R2 = 0.988, where x represents nitrate concentrations （〈40 btmol/L） and y represents the Nrt2 transcript levels.

Nitrate contamination in groundwater of Kabul Province,Afghanistan:Reasons behind and conceptual management framework discourse

Groundwater contamination has been on the rise in Afghanistan.It has become a major concern among the policy makers.This paper aims to propose practical options for the management of nitrate contamination in one of Afghanistan’s groundwater polluted provinces,Kabul.The management framework utilized Mann-Kendall and Sen Slope tests to detect nitrate trend and geostatistical analysis option in Arc GIS 10.5 to assess the nitrate change.To explore the impact of various management options,a number of legislative documents were reviewed.The results indicate a decline in the nitrate storage of Kabul aquifers from 108 mg/L in 2005 to 0.044 mg/L in 2010.Considering the whole period of the study,the results show that the nitrate volumes remain lower than the nitrate concentration range proposed by World Health Organization(50 mg/L).Groundwater dynamics in Kabul aquifers were influenced by nitrate derived from precipitation and nitrate input from root zones in agricultural areas.Finally,different management options for groundwater pollution from nitrate and corresponding authorities,incorporated urban,rural and agriculture,were proposed.It is expected that this study will help policy makers to better manage the nitrate storage of Kabul aquifers by implementing the proposed management options.

A modified active disturbance rejection control for a wastewater treatment process

Waste water treatment process(WWTP)control has been attracting more and more attention.However,various undesired factors,such as disturbance,uncertainties,and strong nonlinear couplings,propose big challenges to the control of a WWTP.In order to improve the control performance of the closed-loop system and guarantee the discharge requirements of the effluent quality,rather than take the model dependent control approaches,an active disturbance rejection control(ADRC)is utilized.Based on the control signal and system output,a phase optimized ADRC(POADRC)is designed to control the dissolved oxygen and nitrate concentration in a WWTP.The phase advantage of the phase optimized extended state observer(POESO),convergence of the POESO,and stability of the closed-loop system are analyzed from the theoretical point of view.Finally,a commonly accepted benchmark simulation model no.1.(BSM1)is utilized to test the POESO and POADRC.Linear active disturbance rejection control(LADRC)and the suggested proportion-integration(PI)control are taken to make a comparative research.Both system responses and performance index values confirm the advantage of the POADRC over the LADRC and the suggested PI control.Numerical results show that,as a result of the leading phase of the total disturbance estimation,the POESO based POADRC is an effective and promising way to control the dissolved oxygen and nitrate concentration so as to ensure the effluent quality of a WWTP.

Assessing the Vulnerability of Groundwater to Pollution Using DRASTIC and VLDA Modelsin Halabja Saidsadiq Basin, NE, Iraq

Groundwater plays important roles as one of the essential source of water supplies of the studied area. Consequently, it needs to be prevented from contamination. In this study, two methods have been examined, namely DRASTIC （depth to groundwater, net recharge, aquifer media, soil map, topography, impact of vadose zone and hydraulic conductivity） and VLDA （vadose zone lithoiogy, land use patterns, depth to groundwater and aquifer media） to model a map of groundwater vulnerability for contamination of the basin. The standard DRASTIC vulnerability maps classified the basin of four vulnerability index zones： very low （34%）, low （13%）, moderate （48%） and high （5%）. While the VLDA model classified the area into four categories as well： low （2%）, moderate （44%）, high（53%） and very high （1%）. The results demonstrate that there is a significant dissimilarity in the rate of vulnerability. Validation of the constructed maps is required to confirm the validity of the theoretical sympathetic of current hydrogeological conditions. In this study, nitrate concentration analysis was selected as a contamination indicator to validate the result. The nitrate concentration of two different seasons （dry and wet） was analyzed from （30） watering wells, considerable variations in nitrate concentration from dry to wet seasons had been noted. Consequently, it points toward that groundwater in the HSB （Halabja Saidsadiq Basin） is capable to receive the contaminant due to suitability of overlies strata in terms of geological and hydrogeological conditions. Based on this confirmation, the result exemplifies that the degree and distribution of vulnerability level acquired using VLDA model is more sensible than that attained from the standard DRASTIC method .In addition, the DRASTIC models need to be modified based on the land use pattern, which clarifies the role of human activity on the vulnerability system.

Groundwater Vulnerability Using DRASTIC and COP Models: Case Study of Halabja Saidsadiq Basin, Iraq

To avoid groundwater from contamination, the groundwater vulnerability tool can be examined. In this study, two methods were applied, namely: DRASTIC (Groundwater depth, Net recharge, Aquifer media, Soil map, Topography, Impact of vadose zone and Hydraulic Conductivity) and COP (Concentration of flow, Overlying layer and Precipitation) to model groundwater vulnerability to pollution. The result illustrated that four vulnerability classes were recognized based on both models including very low, low, moderate and high vulnerability classes. The coverage areas of each class are (34%, 13%, 48% and 5%) by DRASTIC model and (1%, 37%, 2% and 60%) by COP model, respectively. The notable dissimilarity between these two models was recognized. For this reason, nitrate elements were selected as a pollution indicator to validate the result. The concentrations of nitrate were recorded in two following seasons in (30) watering wells;as a result, the substantial variation was noted. This indicates that contaminants can be easily reached the groundwater due to its suitability in geological and hydrogeological conditions in terms of contaminant transportation. Based on this confirmation, the standard DRASTIC method becomes more sensible than COP method.

Nitrate in shallow groundwater in typical agricultural and forest ecosystems in China,2004-2010

The nitrate-nitrogen（NO 3-N） concentrations from shallow groundwater wells situated in 29 of the Chinese Ecosystem Research Network field stations,representing typical agroand forest ecosystems,were assessed using monitoring data collected between 2004 and 2010.Results from this assessment permit a national scale assessment of nitrate concentrations in shallow groundwater,and allow linkages between nitrate concentrations in groundwater and broad land use categories to be made.Results indicated that most of the NO 3--N concentrations in groundwater from the agroand forest ecosystems were below the Class 3 drinking water standard stated in the Chinese National Standard：Quality Standard for Ground Water（≤ 20 mg/L）.Over the study period,the average NO 3--N concentrations were significantly higher in agro-ecosystems（4.1 ± 0.33 mg/L） than in forest ecosystems（0.5 ± 0.04 mg/L）.NO 3-N concentrations were relatively higher（〉 10 mg N /L） in 10 of the 43 wells sampled in the agricultural ecosystems.These elevated concentrations occurred mainly in the Ansai,Yucheng,Linze,Fukang,Akesu,and Cele field sites,which were located in arid and semiarid areas where irrigation rates are high.We suggest that improvements in N fertilizer application and irrigation management practices in the arid and semi-arid agricultural ecosystems of China are the key to managing groundwater nitrate concentrations.

High-performance size exclusion chromatography with a multi-wavelength absorbance detector study on dissolved organic matter characterisation along a water distribution system

This study examined the associations between dissolved organic matter（DOM） characteristics and potential nitrification occurrence in the presence of chloramine along a drinking water distribution system. High-performance size exclusion chromatography（HPSEC） coupled with a multiple wavelength detector（200–280 nm） was employed to characterise DOM by molecular weight distribution, bacterial activity was analysed using flow cytometry, and a package of simple analytical tools, such as dissolved organic carbon, absorbance at 254 nm, nitrate,nitrite, ammonia and total disinfectant residual were also applied and their applicability to indicate water quality changes in distribution systems were also evaluated. Results showed that multi-wavelength HPSEC analysis was useful to provide information about DOM character while changes in molecule weight profiles at wavelengths less than 230 nm were also able to be related to other water quality parameters. Correct selection of the UV wavelengths can be an important factor for providing appropriate indicators associated with different DOM compositions. DOM molecular weight in the range of 0.2–0.5 kDa measured at210 nm correlated positively with oxidised nitrogen concentration（r = 0.99）, and the concentrations of active bacterial cells in the distribution system（r = 0.85）. Our study also showed that the changes of DOM character and bacterial cells were significant in those sampling points that had decreases in total disinfectant residual. HPSEC-UV measured at210 nm and flow cytometry can detect the changes of low molecular weight of DOM and bacterial levels, respectively, when nitrification occurred within the chloraminated distribution system.