To investigate the effect of granular structure on resistance to toxic chemicals in upflow anaerobic sludge blanket (UASB) reactors, normal and broken granules were examined for their ability to degrade acetate with and without the addition of toluene or trichloroethylene as a toxic chemical. Without toxic chemical, both normal and broken granules degraded the acetate at the same volumetric degradation rate $(3.21 mM·h^{-1}). However, When 500 $μl·l^{-1}$ of toluene or trichloroethylene was added, the acetate-degradation rate of the broken granules was about a third of the rate with normal granules. Therefore, the layered structure of the UASB granules seems to give microbial populations the ability to resist toxic chemicals.
Effect of the granulation in the UASB reactor was studied in order to select the most optimal anaerobic microbial population to resistant toxic materials. Metal ions $(Cd^{2+}, Cu^{2+}, Ni^{2+}, Zn^{2+} and Cr^{3+})$ on anaerobic digestion with intact and disintegrated granules from a UASB reactor did not affect glucose degradation or the production of methane. However, when $Cu^{2+} was at 500 mg/g-VSS (volatile suspended solids) in the media, the glucose degradation rates and methane production rates decreased by 14% and 32% in disintegrated granules, respectively, whereas, in intact granules, decreases were 3% and 14%, respectively. When various electroplating metal ions were tested, 50% inhibition of acetate degradation and methane production were produced by 210 - 770 mg/g-VSS and 120 - 630 mg/g-VSS, respectively. The relative toxicity of the electroplating metals on methane production was in the order of $Zn^{2+}$ (most toxic) ＞ $Ni^{2+} ＞ Cu^{2+} ＞ Cr^{3+} ＞ Cd^{2+}% (least toxic).
In the acetate degradations test of UASB granules with $Cu^{2+}$, all of the acetate disappeared was not converted to methane, stoichiometrically. To study how much acetate was used by the other microorganisms except methanogens, reduction of nitrate and sulfate was investigated in the various concentrations of $Cu^{2+}. The missed acetate was consumed in sulfate reduction and denitrification by sulfate reducing bacteria (SRB) and nitrate reducing bacteria (NRB) in the granules, respectively. Considering that the granules reduced nitrate and sulfate by 3.3 mM and 5.4 mM, respectively, about 18% of the initial acetate could be converted stoichiometrically to $CO_2$. In conclusion, SRB and NRB had more resistance to $Cu^{2+}$ than methanogen so that in certain range of metal concentration difference between acetate degradability and methanogenic activity occurred.
Real wastewaters such as landfill leachate and swine wastewater were treated with intact and disintegrated granules from a UASB reactor. Although swine wastewater test showed that intact and disintegrated granules had about the same degradation rate, landfill leachate was more rapidly degraded by intact granules. This result implied that landfill leachate contained more toxicants than did swine wastewater. Utility of UASB granulation to treat various wastewaters was investigated. The relative utility of the granulation on the treatement of wastewaters was in the order of landfill leachate ＞ dyeworks wastewater ＞ food wastewater ＞ swine wastewater ＞ municipal wastewater ＞ synthetic wastewater. This result implied that landfill leachate contained the most toxicants than any other wastewater tested.
Synthetic wastewater and landfill leachate was continuously treated with UASB reactor at 30°C. The disintegrated granules as well as intact granules were inoculated at initial time. COD removal efficiency of synthetic wastewater with normal granules achieved was fairly consistent in the range of 81 - 87% at the organic loading rate (OLR) of 0.5 kg COD ㎥/day. With broken granules at the same condition, COD removal efficiency achieved was in the range of 76 - 83%, showing that this process is very promising for the anaerobic treatment of low-strength wastewater, such as municipal and domestic wastewater. After alteration of OLR to 1.0 kg COD ㎥/day, the loading shock that decreased the COD removal rate was observed at all the reactors irrespective of granular state and types of wastewater. However, the reactors with intact granules has recovered the COD removal rate up to 90% in 10 days in the treatment of both of the synthetic wastewater and landfill leachate. When the OLR was increased to 2.0 kg COD ㎥/day, loading shock was observed, too. However, the recovery of the COD removal rate took the longer time than the loading shock of the OLR 1 kg COD ㎥/day. When the diluted wastewater of COD 5000 ppm which was a quarter of COD of the real landfill leachate was used for the influent, disintegrated granules were slowly flocculated, showing the similar COD removal rate as intact granules. This result implied that the granulation of the UASB reactor was helpful for the treatment of toxic wastewater like landfill leachate.
손상되지 않은 입상슬러지를 이용한 포도당 발효실험에서는 구리의 존재 유무와 관계없이 분해율이 거의 일정하였다. 구리가 존재하지 않은 경우에는 분쇄된 입상슬러지와 원 입상슬러지의 VFA 분해와 메탄 발생량은 차이를 보이지 않았으나 구리가 500 mg/g-VSS 존재하는 경우 분쇄된 입상슬러지의 경우 VFA 분해와 methane 발생이 상당히 저해되는 것을 알 수 있었다. 구리의 농도가 100 mg/g-VSS 미만인 경우에는 그 구조에 의해 영향을 받지 않고 12시간 안에 acetate가 완전히 분해되었으며 methane 생성량도 거의 변화가 없었다. 그러나 구리의 농도가 100 mg/g-VSS를 넘어감에 따라 methane 생성량이 급격히 감소하였다. 구리의 농도가 두배 늘어남에 따라 methane production rate는 2.88 mM/h에서 2.12와 1.95로 각각 감소하였으나 acetate 분해(각각 3.07, 2.78)는 초기 acetate degradation rate(3.33)에 비해 저해가 별로 되지 않음을 알 수 있었다.
다양한 중금속이 granule에 미치는 영향을 살펴보았을 때, acetoclastic 활성에 미치는 독성효과는 Zn(가장 독성이 높음) ＞ Ni ＞ Cd ＞ Cr(가장 독성이 낮음)과 같은 순서를 메탄 생성 활성에 미치는 독성효과는 이와는 약간 다르게 Zn(가장 독성이 높음) ＞ Ni ＞ Cr ＞ Cd(가장 독성이 낮음)로 나타났다.
Acetate를 포함한 폐수처리시 유기독성물질의 영향에서도 전체적으로 trichloroethylene의 저해력이 toluene보다 큰 것을 알 수 있었고, 이에 반해 toluene에서의 저항능력의 차가 오히려 trichloroethylene보다 큰 것을 나타내었다. 특히 독성물질 함유농도 50 ppm까지는 거의 나타나지 않던 normal granule과 broken granule 의 아세테이트 제거능력이 차가 100 ppm부터는 나타나기 시작하여 500 ppm에서 최대가 되었다. 그러나 저해물질의 함유농도가 5000 ppm 이상인 경우에는 그 차이가 거의 나타나질 않았고, 이는 100 ppm에서 1000 ppm 사이에 critical point가 존재한다는 것을 알 수 있다. 실험에 사용되어진 입상슬러지는 맥주공장 슬러지에서 샘플링되어서 비교치가 오히려 작을 것으로 예상되며, 독성물질을 다량 함유한 산업폐수처리 공장에서 운용되는 UASB 반응기에서 샘플링되는 입상슬러지는 그 비교치가 더 클 것으로 예상된다.
반응기운전에서는 인공폐수와 침출수를 각각 COD 1000 mg/l로 운전하도록 조작되었다. 초기 유입폐수의 COD 제거율이 급속히 상승하는 것을 관찰한 후, 곧 COD를 2000 mg/l로 유지시켜 반응기를 운전하였다. 전체적으로 Intact granules의 COD처리능력이 disintegrated granules의 능력보다 우수한 것을 알 수 있었고, 이는 인공폐수에서는 큰 차이가 보이지 않는데 비해, 침출수 처리에서는 큰 차이를 보여 serum bottle test와 동일한 결과를 나타내었다. 그러나, 30일 이후 HRT를 1day로 낮춘 후, 제거율은 큰 폭으로 떨어지는 것을 알 수 있었고, 이를 회복하는데는 상당한 시간이 걸렸다. 48일 이후, COD제거 능력이 일정 수준 회복되는 것을 관찰한 후, 실폐수의 COD의 4분의 1 수준의 COD 5000 mg/l로 폐수를 반응기에 투입하였다. 이때도, 앞에서 보여주지 않았던, load shock이 발생하는 것을 알 수 있었다. 이후, 60일이 경과하자 COD제거율은 일정 수준 회복하는 것을 알 수 있었다. 특이한 점으로 60일 이후에서 disintegrated granule에서 미세하나마 sludge의 flocculation이 일어나는 것을 관찰할 수 있었고, 이는 반응기에 투입된 침출수의 처리에 도움이 되었으리라 예상할 수 있다. 즉, 반응기에 투입된 다양한 폐수의 성상에 granulation은 무시할 수 없는 중요한 인자로 규명되었다.
