Remediation of static lake water by intensified filter of dominant bacteria colony

LIU Shu-yu，MA Fang，WANG Fan，ZHANG Jie

劉書宇， 馬 放， 王 帆， 張 杰

(1.School of Environment and Chemical Engineering，Shanghai University，Shanghai 201800，China;2.State Key Laboratory of Urban Water Resources and Environment，Harbin 150090，China;3.College of Environmental and Chemical Engineering，Dalian University，Dalian 116622，China)

Eutrophication is an important contamination problem which can affect water supply broadly［1－2］.Many problems occurs，such as fisheries declining［3－4］，and aquatic vegetation losing［5］.Eutrophication also causes many biological responses［6－7］.Some physical，chemical and biological methods have been used in water remediation［8－11］. Their problems include expensive cost［12］，inefficient removing effect of physical methods and second environment contamination of chemical technique.Enhanced biological is also expected to improve the removal of a high percent of nutrient.

As a major path for ammonia removal［13］，nitrification and denitrification depends on microbe in the filter system［14］，which is limited by oxygen conditions.Oxidation of ammonia to nitrate is often controlled by insufficient oxygen.Constructed wetland technology is currently evolving into an acceptable，economically competitive alternative for many wastewater treatment applications［15］.Although carbonaceous materials can be removed from wastewater very well，nitrification needs long hydraulic retention times in conventional filter treatment systems for nitrogen removal［16］.So，a kind of new ecological filter is constructed and dominant bacteria colony is applied in order to improve nitrogen treatment efficiency.

1 Material and Methods

1.1 Materials

Zeolite and coal cinder are chosen as the main materials in this study.They are made up the filler of the filter bitch instead of conventional fillers.Zeolite has the ability of adsorbing ammonia nitrogen for its high specific surface areas and high cation exchange capacities(CECs).Their rigid three-dimensional structures make them shrink and swell free.So，it can offer superior sorption and hydraulic properties and be used as molecular sieves and sorbents in wastewater treatment［17－18］.Zeolites have been particularly useful in removing cationic species，such as ammonium and some heavy metals from water.It is permeable reactive media for contaminant removal.Chemical and biological method can be used for regeneration of zeolite.

Coal is an important energy source for most parts of the world.As a consequence of its use，there are estimated to be approximately 500 million tons of coal ash and cinder produced globally every year.Of this amount，less than one-quarter is used commercially，with the rest being disposed in landfill.The study has shown that coal ash has some absorption capacity.Be nch-scale laboratory experiments and full-scale field tests show its capacity of phosphorus removal［19］.

Fig.1 shows the ecological filter construction in the experiments.The length，width，height of the ecological filter are 150 cm，40 cm and 30 cm，respectively.Coal cinder with 5 cm thickness is put at the bottom;zeolite with 15 cm thickness is put in the middle，and sand with 10 cm thickness is put on the top.Clapboard is set vertically in the middle of the filter.The filter is divided into two parts by the clapboard.

Fig.1 Construction of the ecological filter

1.2 Running Manner

Hydraulic direction is shown as the arrowhead.1，2，3 and 4 are sampling sites in Fig.2.Sampling begins when the last NH4+-N concentration of effluent keeps steady.Water speed is controlled to make its retention time in the filter with 1 h，2 h，and 4 h respectively.

Fig.2 Hydraulic direction and sampling site

1.3 Dominant Bacterium Colony Domesticating

Four polyphosphate accumulating bacterium named L17b1，L17b2，L19y，L19w are screened out from lake water.Their phosphorous accumulating rates are all more than 60%.All the bacterium including four nitrous bacterium(H1，H8，H8 and ZW’)are domesticated by dilution method and cultured together.The proportion between nitration bacterium，nitrite bacterium and polyphosphate accumulating bacterium is 1∶2∶1.They are fixed into filter box until the total number of bacterium reaches about 108/L.The filter is aerated for 72 h with 12 h interval.Abundant bacteria live in the cavities of the zeolite and they become the dominant colony in the water treating process.This system is D system.As a contrast system，aboriginal bacterium colony in the lake water is domesticated and attached in A system.N system has no additional bacterium attached.

1.4 Analysis Method and Water Quality of Influent

The contaminated water comes from a eutrophicated lake located at 45°45'N，126°38'E in Northeastern China every July.The quality of influent water is shown in Tab.1.The pollutants include ammonia nitrogen(NH4+-N)，total nitrogen(TN)and total phosphorus(TP).NH4+-N and NO2－-N is analyzed by 722-spectrophotometer，and TN is analyzed by Nitrogen Measuring Unit，and TP is analyzed by CP-OES and TOC by Organic Carbon Analyzer(VCPN).

Tab.1 Water quality of influent

2 Results and Discussion

2.1 Removal Rates of NH4+-N，TN and TP

As shown in Tab.2，NH4+-N removal efficiencies in three systems are all more than 75%and increase with retention time.Removal efficiencies of NH4+-N in N system are all more than 90%and when the rest time is 4 h，it is 98.5%for strong adsorptions ability of NH4+-N by zeolite.In D system，it is better than that in A system，and that portion of NH4+-N is transited by mass of ammonia oxidation bacterium and nitrite oxidation bacterium［20－21］.

In N system，TN removal efficiency decreases from 52.2%to 30.4%with the change of water retention time.In A system，it increases from 10.1%to 15.8%slowly.In D system，it increases to 71.5%from 54.9%.In D system，part of NH4+-N is nitrified to NO2－-N and NO3－-N by functional bacterium colony.When retention time prolongs，anaerobic condition leads to denitrification.In A system，nitrite cannot be nitrified greatly.Little bacterium lives in N system，which makes TN removal hard.TN removal efficiency increases with retention time through the change of NH4+-N.

TP removal efficiencies increase with retention time.In A system，it is much higher than those in the other two systems.It is from 94.2%to 96.7%.It is from 73%to 79.8%in D system.In N system，it is lower.The removal process depending on PO43－combining with Al3+，Ca2+，Mg2+in system is a slowly process.In D system，mass of bacterium improve TP removal efficiency，such as polyphosphate accumulating bacterium.A system has little polyphosphate accumulating bacterium.But the removal efficiencies are all more than 94%，abundant aboriginal bacterium advance phosphorus removal，and the effect is better than single functional bacteria.

Tab.2 Removal rates of NH4+-N，TN and TP(N system，A system，D system)

2.2 Change of Different Nitrogen Contamination Concentration

In Fig.3，hydraulic retention time is 2 h.The influence runs downwards to#1，and then flows to#2，and then to#3，finally upwards to#4.In N system，NH4+-N concentration is the lowest at each site.In A system and D system，ion exchange of NH4+-N is cut down by mass of bacterium on the surface of zeolite，and nitrification is not completed.In D system，NH4+-N concentration decreases evidently at#4 for higher oxygen concentration.Then，nitrifications promote NH4+-N removal.

The change of NO2－-N concentration is shown in Fig.3(b).NO2－-N concentration in N system is the least among three systems.In A system，NO2－-N concentration do not change obviously，not much nitrite transition bacterium to be existed，so NH4+-N cannot be transited to NO2－-N.In D system，NO2－-N concentration increases from#1 to#2，and it decreases from#3 to#4，concurrence of much ammonia oxidation bacterium and nitrite oxidation bacterium nitrify some NH4+-N，NO2－-N as the middle production is formed.In#4，oxygen concentration is higher，and nitrification is stronger，so more NO2－-N is transited to NO3－-N，and NO2－-N concentration at this site decreases.

The change of TN concentration is shown in Fig.3(c).In N system，TN concentration decreases at#1 site.TN is mainly composed of NH4+-N，and its removal depends on zeolite adsorption.But，in the flowing sites，ion exchange is main action.In D system，nitrogen removal depends on nitrite oxidation bacterium，and biological action do not affect it much，so TN concentration declines slowly at#1 and#2 sites，but fast at#3 and#4 sites.

Fig.3 Change of contamination concentration at each sampling site

2.3 Nitrogen Transition and Accumulation Process

Nitrogen transition along hydraulic distance is very important for studying its removal process.It is mainly being composed of two parts，ion exchange and nitrification.

Ion exchange reaction can be expressed as follows:

2NH4++NaX→NH4X+Na+

Nitrification reaction can be expressed as follows:

The addtion of NO2－-N and NO3－-N concentration indicates the removal part by nitrification，reduction of total inorganic nitrogen including NH4+-N，NO2－-N and NO3－-N indicate the removal part by ion exchange.

The removal efficiencies of NH4+-N are expressed individually as follows:

TRE(total removal efficiency)=(CNH4+，i-CNH4+)/CNH4+，i×100%

IRE(removal efficiency of ion exchange)=(CTN，i-CTN)/CNH4+，i×100%

NRE(removal efficiency of nitrification)=(CNO-CNO，

Ciand C are the concentration of inflow and the edge respectively.TN=NH+-N+NO－-N+NO－-

Removal efficiencies by ion exchange in each system are shown in Tab.3.NH4+-N removal efficiency by ion exchange reaches 67.1%in short time，and it changes to 73%，53.1%and 47.4%at#2，#3 and#4 respectively.The change of oxygen concentration and contamination concentration affects the ion exchange.In contrast，ion exchanges in A system at#1 and 2#are 45.6%and 35.2%individually，going down to 9.9%then up to 18.8%at 3#and 4#.In A system，aboriginal bacterium form a layer of film on the surface of the filler，so ion exchange is blocked.In D system，ion exchange efficiencies are only 18.9%and 24.4%at#1 and#2 sites，and it increases to 51%then to 58%at#3 and#4.Functional bacterium consortium adsorbs much NH4+-N in short time and reserves it in the film，and ion exchange is prolonged.With the extension of contacting time，NH4+-N penetrates through the film，so ion exchange efficiency increases.

Tab.3 Removal efficiency of nitrogen by ion exchange along hydraulic distance

Removal efficiencies by nitrification in each system are shown in Tab.4.In N system，nitrification efficiency increases slowly from 16.6%to 18.2%，and to 22.7%at#3 site，then to 24.2%at#4 site.Little bio-stratum forms during contaminated water flowing，with its resting time in system，nitrification increased up steadily.

In A system，nitrification efficiency was 18.9%at#1，higher than that in N system.The highest nitrification efficiency was 20.1%at#2 site，and then it decreases to 9.3%at#4 site.A mass of bacterium live in A system，and nitrification is stronger than that in N system at the beginning.But for its complex composition，nitrate bacterium is not dominant，so nitrification is instable.

In D system，nitrification efficiency keeps raising from#1 to#4 site.It is lower than those in other two systems at the beginning.It is 29.2%at#4 site.High concentration of oxygen is one main reason，and a mass of nitrite and nitrate bacterium keep high activity，when contacting time is prolonged，nitrogen removal efficiency by nitrification increases.

Tab.4 Removal efficiency of nitrogen by nitrification along hydraulic distance

3 Conclusions

1)NH4+-N removal efficiency in D system is better than those in the other two systems for zeolite absorption，and TN removal efficiency is also higher.Nitrite and nitrate bacterium keep high activity when contacting time is prolonged，and nitrogen removal efficiency by nitrification increases.Functional bacterium consortium can adsorb much NH4+-N in short time and reserve it in the film，and ion exchange is prolonged with contacting time extending.Most nitrogen removal is hastened through nitrification by abundant nitrous and nitride bacterium in dominant colony.That dominant consortium keeps high activity in long time.

2)Phosphorus removal is improved by abundant aboriginal bacterium.Complex functional bacterium is benefit to decompose organic phosphorus and its removal.

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