Chinese report of LEVAPOR field-tested

 

Entrance to the NINGAN Sewage Treatment Plant

INTRODUCTION

 

NINGAN is a city with 440.000 inhabitants located ca. 20 km southwest of Mudanjiang in the Heilongjiang province . Due to the cold climate in the area and our positive experiences in the biotreatment of municipal sewage in LEVAPOR supported fluidized bed reactors in Northern Europe, it has been decided to use this technology also in one new municipal plant of Ningan, designed for a capacity of 22.000 m³/day wastewater.produced with a hired device and staff. The biocarrier have been produced on-site and poured directly into the aerated basin.

 

Fig. 1 LEVAPOR biocarrier

 

DESIGN AND STARTUP

The plant has been designed and constructed by a local company Harbin Baishenglubin Environmental Technology Co.Ltd, without primary sedimentation, comprising of 4x800 m³, resp.3.200 m³ aerobic basins, corresponding with hydraulic retention times between 3,5 and 3,8 hours, with 6,0 m water depth aerated by porous membrane aerators and filled with 400 m³ (ca. 12,5 vol.%) LEVAPOR biocarrier cubes of 20x20x7 mm.

Fig. 2 Filling the reactor Fig. 3 Fluidised LEVAPOR carrier in the basin

 

The plant was started in October 2010, in Mudanjiang usually the beginning of winter, without seeding it with nitrifying sludge and reached quite fast its full COD removal capacity, while the start and establishment of nitrification required opposite to experiences in Europe several weeks. The reason for the delay was, that in Europe an existing plant with already established suspended nitrifiers was upgraded, while in the new plant in China the development of slowly growing nitrifying bacteria and their establishment within heterotrophic sludge flocs required more time.

 

 

PERFORMANCE OF THE PLANT

Complete results have are available since September 2012 , this presentation covers the results of the period of a complete year, from December 2012 until November 2013 , characterized by remarkable fluctuations of inlet COD- ( 140 570 mg/L) and N- (18 - 55 mg/L) concentrations as well as the usual seasonal course of water temperatures between

5°C and 20°C).

 

COD removal

Due to the average results of the period October December 2012 are presented in table 1.

Legend

Dimension

Value

Volume of reactors

3200 (4 x 800)

Volume LEVAPOR

400 (12,5 %)

Hydraulic ret. time

h

3,5 – 3,8

2012

October

November

December

COD in

out

mg/L

mg/L

294

33,7

295

35,8

302

37,7

BOD5 out

mg/L

11,9

12,9

12,9

TN in

TN out

NH4N out

mg/L

mg/L

mg/L

28,8

12,5

2,0

35,3

14,8

3,2

23,2

11,0

3,34

Water temperature

°C

15,6

13,3

9,6

 

Table 1. Technical data and performance of the WWTP in Oct.- Dec. 2012.

Fig. 4 COD removal in the period of December 2012 November 2013

 

the plant achieved despite to the winter period at water temperatures between 6°C and 10°C in December very high COD- , BOD- and N-removal rates, maintaining them also over the following 12 months, practically independent of the water temperature and inlet COD concentrations, as shown in Fig, 4 and especially Fig. 5.showing that outlet COD is

 

Fig. 5 Outlet COD concentrations and water temperatures over the year in 2013

 

fluctuating within relatively narrow concentration limits, not depending on inlet COD concentrations (and vol. loading rates ) as well as temperature fluctuations between + 6°C and +20°C. Fig. 6 documents the same observations, showing the results of a period with

Fig. 6 COD-values between May 5. and May 22., the period with highest inlet COD

 

intensive fluctuations of inlet COD at relatively high concentrations. Within 9 days (10 - 19) with relatively high

average inlet COD of 401,4 mg/L and Lv = 2,53 kgCOD/m³ *d, the average outlet COD is 38,8 mg/L or 90,3 % removal, while during the 3 days (17-19) with

highest inlet COD of 516 mg/L and Lv = 3,3 kgCOD/m³ *d the outlet COD is 42,3 mg/L, meaning 91,8 % COD removal.

During the same period 35,3 mg/L inlet TN ( Lv ~ 223 gN/m³ *d) have been nitrified without any problem to a final effluent polluted with 2,9 mg/L NH4N and 12,1 mg/L TN-out.

 

 

Nitrogen removal

Due to the high sensitivity of the slowly growing and settling, non flocculating nitrifying bacteria to changing temperature, pH, salinity and certain pollutants, the nitrification represents the main problem of the biological nutrient removal processes.The immobilisation of nitrifying biomass and nitrification by biofilm technologies represents one of the best and economic method for a successful a stable process, because especially nitrifying bacteria tend to build biofilms, enabling a faster establishment of the required quantity of active biomass in the bioreactor.

Due to the lack of inoculation,seeding the reactors with initial active nitrifying bacteria, after several months a stable nitrification was established.As result of the high porosity, large inner surface of LEVAPOR carrier and lower redox potential within the cubes, within the aerated basin, additionally a further process, typical primarly for porous carrier like LEVAPOR, the simultaneous aerobic denitrification has been established.

Fig. 7 Nitrogen removal at NINGAN STP between Dec. 2012 and Nov. 2013

 

Results, presented in Fig.7 show that except two disturbances of the nitrification process, caused by longer influence of lower pH-values in the range of pH 6,4 -6,6 (resulting of nitrification) both, a successfull and stable nitrification as well as a remarkable simultaneous denitrification took place over the whole 12 months, including winter period, whereby the not yet investigated denitrification showed fluctuations, depending probably on COD:N-ratio , loading rates, etc.

It is important to register, that under stable conditions, the biofilm oxidized also inlet TN concentration of 45 to 50 mg/L, what is in the range of remarkably high N-vol. loading rates of Lv ~ 290 to 310 gN/m³ *d !

The quite low TN-out concentrations mean, that in the biofilm a remarkably denitrification takes place, whereby the difference of outlet TN and outlet NH4N, might be residual NO3N .

In order to obtain more reliable results during the analysis of those bioprocesses, average values of ca. 40 selected sequences of 5 to 15 successive days with similar results were calculated and used for calculations.

Fig. 8. Outlet TN- and NH4N-concentrations at different phases

 

As fig. 8 shows, in the case of stabile nitrification, outlet NH4N concentrations of < 5,0 mg/L

and TN in the range of 12 to 20 mg/L can be obtained even at low temperatures,however in the case of required lower NO3N values, via installation of a compact post-denitrification also this parameter can be reduced totally. Quantifying the mentioned figures, it can be concluded that additionally to the usual degrees of nitrification in the range of 80 to 96%, also a significant and stable removal of 40 to 70 % Ntotal via aerobic denitrification takes place.

Fig.9 Degree of nitrification and TN-removal in different phases of 2013

 

 

Temperature dependence of nitrification rates

It is known that rates of biodegradation reactions follow van´tHoff Arrhenius´ empirical formula of the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10 °C.

Fig.10. Temperature dependence of volumetric N-loading- and nitrification rates

 

Despite to fluctuating and at higher temperatures increasing inlet-N concentrations the analysis showed the temperature dependence of volumetric N- loading rates LvN (gN/m³ *d) and nitrification rates VN (g Nox/m³ *d). Due to the data presented in Fig. 10. the temperature dependence is evident, however the achieved nitrification performance was despite to fluctuations of inlet-N concentrations and temperatures remarkably better then the performance of activated sludge systems.

 

Temperature

Vol.loading rate, LvN

N-oxidation rate

N-oxidation

°C

g N /m³ *d

g Nox. /m³ *d

%

17 - 20 °C

293

275

93,9

11-13°C

218

187

85,8

8-10 °C

194

166

85,6

5 - 7 °C

188

152

80,9

Tab. 2 Temperature dependence of volumetric N-loading and nitrification rates

 

 

Conclusions

1.Despite to decreasing temperatures and remarkably shorter hydraulic retention

times in the bioreactors of 3,5 to 3,8 hrs (instead of usual 6 to 10 hours), the plant

showed very good results,achieving outlet COD-values of 33 to 40 mg/L (88 89%)

and oulet-NH4N-values of 2,0 to 3,3, mg/L (91- 93 %),meeting all legal requirements.

2.Despite to remarkable fluctuation of the inlet-COD and TKN concentrations,

performance of both processes remained stable, a significant dependence of

declining temperatures, typical for nitrification has not yet been registered,

confirming earlier experiences.

3.The relatively high removal of TKN confirmes also that a remarkable amount of

generated nitrate (NO3-) became denitrified within the porous carrier body,with

locally lower oxygene concentrations.

4. The results confirmed all advantages of biofilm technology and show that appli-

cation of this technology enables efficient and stable problem solutions at

significantly lower capital and operation costs.

5. As basis for designing STP´s on biofilm basis

5.1. On COD loading rate Basis : 3,2 to 3,5 kg COD/m³ *d , respectively

5.2. On TKN-loading rate Basis : 200 to 250, eventually also 300 gN / m³ * d

can be taken in account

 

Presented informations are based on experiences with application LEVAPOR carrier. Testimonies on expected effects can be made in individual case only on basis of investigations of given emissions and in some cases on basis of practice relevant experiments.