08.08.2015   BIOMASS NOW - CULTIVATION AND UTILIZATION

Hybrid bioreactor mathematical modeling

The mathematical modeling is a very useful method of process simulation, because there is no need time and costs consuming experimental methods using. However, there are many problems in adequate mathematical description of complex biochemical processes and parameters’ estimation.

For hybrid bioreactor modeling the ASMH1 model [11] can be applied. It is based on the ASM1 model, but significantly modified: nitrogen removal processes are more completely treated by implementation of two stages nitrification and denitrification (figure 14). The intermittent aeration and oxygen accessibility to the second phase of nitrification was

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The model calibration using laboratory data allowed to identify the kinetic and stechiometric parameters values. The model was implemented in to the POLYMATH program and relatively good agreement with experimental results was achieved (st. dev. 10%).

4. Conclusions

The basic technological parameters related to removal efficiency of pollutants from septic tank in hybrid MBBR, at intermittent aeration, continuous/sequencing flow and elevated pH were presented in table 3. The parameters’ values concerning the purified sewage fulfill the Polish law requirements for 2000 p. e. WWTPs.

The hybrid MBBR has occurred an effective system for carbon and nitrogen compounds removal from septic tank effluent. The carbon and nitrogen compounds can be removed

with at least 80% and 50% removal efficiency respectively. It can be achieved even at loading of 2 g COD/gdmd and 12 hours HRT. Similar results were reported by [53] for partial nitrification-denitrification process in combination of aerobic and anoxic reactors with Kaldnes carriers. The system needed internal recirculation. Thanks to attached biomass the nitrification process in the hybrid MBBR was effective at low and high loaded reactors. The remaining of ammonium nitrogen in treated wastewater appeared at high loadings only. The intermittent aeration and dissolved oxygen limitation enabled simultaneous nitrification — denitrification process (SND) in one reactor. The inhibition of second phase of nitrification by free ammonia has intensified nitrogen removal and resulted in energy savings and internal source of carbon using as a sole source. The shortened process of carbon compounds removal was confirmed by medium products appearance. The long time aeration cycles and long time operating cycles can result in denitrification disturbances due to the organic substances oxidation and limitation of that energy source for denitrifying bacteria.

Parameter

Continuous flow reactor CFR

Batch reactor

CFR with increased pH

Pollution load

-organic compounds, g COD/d — nitrogen compounds, g Ntot/d

19.29 — 29.25 5.93 — 6.42

15.56 — 31.57 2.77 — 7.87

26.51 — 27.89 7.30 — 8.25

Hydraulic load, dm3/dm3d

1.53 — 1.90

1.65 — 3.05

1.85 — 2.04

Concentration in purified sewage

-organic compounds, g COD/m3 — nitrogen compounds, g Ntot/m3

26.91 — 56.22 21.57 — 31.07

31.31 — 59.46 27.49 — 34.94

23.00 — 37.00 17.10 — 25.28

Biomass:

-activated sludge density, g/dm3 — biofilm mass, g/m2

0.62 — 1.18 2.58 — 5.46

0.48 — 4.03 0.62 — 3.70

5.58 — 6.52 1.55 — 3.58

Biomass loading of — organic compounds, g COD/gdmd — nitrogen compounds,

g Ntot/gdmd

0.247 — 0.945 0.067 — 0.201

0.081 — 1.080 0.011 — 0.155

0.075 — 0.082 0.011 — 0.021

Efficiency of removal,% — organic compounds — nitrogen compounds

75 — 84 37 — 54

69 — 82 20 — 35

80 — 87 51 — 68

Pollution removal rate — organic compounds, g COD/gdmd — nitrogen compounds,

g Ntot/gdmd

0.206 — 0.663 0.030 — 0.113

0.110 — 0.620 0.004 — 0.032

0.064 — 0.124 0.011 — 0.021

Yield coefficient, gdm/gCODrem

0.31 — 0.43

0.42 — 0.50

0.34 — 0.47

Table 3. Technological parameters and treatment efficiency in hybrid reactors

The pH elevation brought about higher treatment efficiency. The higher volumetric fraction of moving media (carriers) — the better performance. The continuous flow reactor was more effective in treatment and more stable than the sequencing batch reactor.

It was stated and statistically confirmed that: aeration regime, biomass loading and media volume fraction have an impact on the pollutants (especially organic compounds) removal efficiency.

Advantages of hybrid MBBR reactors operating in the modified conditions are as follows: lower energy consumption (up to 40%) related to the shorter aeration time, possibility of specific wastewater treatment (low N/C ratio), simultaneous processes maintaining in one reactor (internal recirculation elimination), overloading resistance (stable performance) and reduction in smaller reactors’ volume. The mathematical model ASMH1 allows to simulate the reactor performance at the specific conditions.