1、CONDITIONS AND MECHANISMS AFFECTING SIMULTANEOUS NITRIFICATION AND DENITRIFICATION IN A PASVEER OXIDATION DITCH Abstract Simultaneous nitrification and denitrification in a Pasveer oxidation ditch was studied.The purpose was to evaluate the performances of both nitrification and denitrificaion in ox
2、idation ditches,and to pursue some possible approaches to enhance nitrogen removal.Almost complete nitrification was observed under normal conditions,but when DO1.0mg/l and /or T 4 ,nitrification was profoundly affected.Also because of low temperature,transient nitrite accumulation appeared on two o
3、ccasions.It was concluded that for nitrification there was a strong capacityto absorb shock nitrogen loading .However,denitrification was unstable and poor；The average efficiency of nitrogen removel was only 45% during a study period of almost 10 months.The bottleneck to denitrification was attribut
4、ed to the lack of stable anoxic zones and carbon compounds available to denitrifiers.Several technical approaches are strongly proposed to improve denitrification. Keywords:Nitrification,denitrification,Pasveeroxidation ditch,anoxic zones,flocs,mixed liquor, dilution factor,fibrous carriers,contacts
5、,contact tank. NOMENCLATURE DO:Dissolve oxygen（ mg/l） , T:Temperrature（ ） , p.e.:Population equivalent, SS:Suspended solid（ mg/l） , MLSS:Mixed liquor suspended solid（ mg/l） , MLVSS:Mixed liquor volatile suspended solids（ mg/l） , COD:Chemical oxygen demand（ mg/l） , BOD5:5-day biochemical oxygen deman
6、d, HRT:Hydraulic retention time（ h） , SRT:Solids retention time（ days） , Kj-N:Total Kjeldahl nitrogen（ mg N/l） , TN:Total nitrogen（ mg/l） , SVI:Sludge volume index（ ml/g） , SV%:Specific volume of sludge settlement for 30 min（ %） INTRODUTION The oxidation ditch process is an economic and efficient te
7、chnique of biological wastewater-treatment. In controlling eutrophication,oxidation ditch are competitive with other activated-sludge processes. Though the Pasveer oxidize the first design speculation of the ditch and can carry on at the same time in diding not hope to make nitric turn respond to tu
8、rn to respond with anti- nitric, oxidize the special structure of ditch and handle the characteristics of the process to has already let this become realistic.In fact, it is many to oxidize the ditches existingly to all have these at the same time two kinds of respond.However,the efficiencies of nit
9、rogen removal differ from place to place. In the framework of international agreement on reduction of nutrients discharge to the river Rhine and the North sea, Holland government puts forward a new restrict to the catchment of the liquid waste processing factory again.In new standard, the total nitr
10、ogen is must be low in 15 mgs/ l in a water. For this, a concerning carry on nitrics turn to respond at the same time in Pasveer oxidize ditch to turns the reaction with anti- nitric of research has already start. This research plan installs for condition and machines that respond synchronously and
11、settle an accommodation, return for increase the nitrogen to do away with the rate to look for the viable path.For this purpose, a study concerning simultaneous nitrification and denitrification in a Pavsser oxidation ditch was initiated. The study was intended to determine the conditions and mechan
12、isms affecting simultaneous nitrification and denitrification. The end conclusion think that rise to decide the function to lie in the upgrade that oxidizes the ditch existingly to Holland and in China of of applied expansion. METHODS Details of process and construction of the Pasveer ditch In the e
13、arly1960s, a pilot-scale Pasveer oxidation ditch was constructed at TNO Delft in the Netherlands for the research purpose of Dr A.Pasveer. The whole system from a single ditch way,a aerating spirit turns to brush,a precipitates the pond, a clarifies the pond, a dehydrates the dry building,a dirty wa
14、ter promotes the pump constitute.A flow diagram is shown in Fig.1. The design volumn of the ditch is 150m3with an average recirculation length of 68.5m； The horizontal piece of the ditch faces to an is on the bottom 3.6 ms, descending the trapezoid of the bottom 1.2 ms. The spirit turns to brush to
15、turn round the round for a level steel, diameter with long distinguish for the 0.7m and 1.5m, respectively.The current capacity is about 400 p.e. The present settler is actually the original thickening tank, which has a circular plan with a diameter of 1.62m and a cone base sloped at 60 to the horiz
16、ontal. The depths of the cylinder and the cone are 1.55m and 0.80m, repectively. The grit chamber is cubic with a total volumn of 40m3； a large diameter water wheel in the chamber slowly rotates to prevent SS from settling. Working conditions The raw wastewater came from a well-define sewer district
17、 of Delft city； the influent, therefore, consisted only of domestic sewage. The influent quality during the study is summarised in table 1. During the study, the influent flow rate was maintained at about 60m3/day； Under thus a discharge, the water power that clarifies the pond carries for the 29 m3
18、/ day, this capacity and ditches that means the clearness pond matches small. Oxidize the ditch in with MLSS and MLVSS to sediments measure among them； The MLSS scope is generally in 10004000 mgs/ l.（ MLSS/MLVSS=0.74） It have no in this operation process to sink the sand to carry on to tidy up usual
19、ly； When admixture the MLSS of the liquid over 4000 mgs/ l also will eject the ditch directly. The earating brush turns to brush an every minute 80 turn of turn soon underwater movement in 1013 cm. Equally again circulating velocity according to dip into the water deep of dissimilarity but settle, m
20、ix with the velocity that the liquid follows the ditch as 0.300.37 m/ s. The sludge loading based on COD was between 0.02 and 0.21 kgCOD/kgMLSSday. According to usual COD/ BOD5 inHolland is 3.0 of ratio, predominate the BOD5 of the dirty mire quantity value be think in the 0.010.07 kg/ kgMLSSDay.This means to oxidize it is very high that SRT in the ditch plant.According to thus an experience:SRT was estimated to be between 25 and 50 days,
