Characteristics Of Acidification And Methane-producing In Anaerobic Baffled Reactor For Treating Animal Carcass Wastewater

Animal carcass wastewater was a kind of high concentration organic wastewater. The accumulation type and level of low molecular organic acid in the process of anaerobic degradation of animal carcass wastewater have a great effect on methane production rate. To achieve effective treatment for animal carcass wastewater and maximize the methane production rate, the anaerobic baffle reactor(ABR) was used to treat the animal carcass wastewater. In this study, it was aim to determine the effect on the common restrictive factors for the anaerobic degradation efficiency of high concentration organic wastewater. The effects of organic loading, hydraulic retention time(HRT) and temperature on the characteristics of acidification and methane-producing were investigated in the ABR reactor. The main results were as follows:(1) In the study of organic loads, the COD removal efficiency maintained 87% or above at organic loading rates increasing from 0.9 to 8.1 g/(L·d). Then the COD removal efficiency decreased to 61% as organic loading rates decreased to 11.9 g/(L·d), and the VFAs accumulation in each compartment of the ABR reactor reached 4320, 3420 and 2510 mg/L, respectively. The VFA accumulation type was mainly presented as acetic acid, and followed by propionic acid and butyric acid. Few isovaleric acid, valeric acid, caproic acid and isocaproic acid appeared as the organic loading increased. The percent contents of acetic acid decreased with the increase of organic loading, while propionic acid and butyric acid were just on the contrary. The treatment effect and methane production rate was optimal at an organic loading rate of 4.6 g/(L·d), The methane production rate of three compartments reached the maximum(0.33, 0.32 and 0.33 LCH4/gCOD). When the organic loading rate was above 8.1 g/(L·d), the accumulation of total VFAs, propionic acid and butyric acid became the inhibitors in the anaerobic methanogenesis process.(2) In the study of HRT, at the HRT of 4, 2, 1, 1/2 and 1/4d, the COD removal efficiency was 94%, 95%, 89%, 53% and 28%, the effluent alkalinity was 4523, 4154, 3465, 4154 and 3465 mg/L, and the VFAs accumulation was 287, 458, 699, 2189 and 3926 mg/L, respectively. Hydraulic shock load caused obvious effects on the reactor operation, the VFAs accumulation of three compartments increased as the HRT decreased. The treatment effect and methane production rate was optimal when the HRT was 2d and 1d. The methane production rate of the first and second compartment obtained a maximum rate at an HRT of 2 d, was 0.307 and 0.321 LCH4/gCOD respectively. The max methane production rate of the third compartment was 0.330 LCH4/gCOD, which was obtained at an HRT of 1d. The Coenzyme 420 content of the first compartment reached the maximum(0.504 μmol/gVSS) at an HRT of 2 d; in the second and third compartment, the Coenzyme 420 content reached the maximum(0.604 and 0.665 μmol/gVSS) at an HRT of 1 d. When the HRT was lower than 1/2 d, methane production rate obviously decreased, the F420 decreased to 0.045, 0.065 and 0.109 μmol/gVSS as the HRT decreased to 1/4 d, methanogenic activity was obviously inhibited. The content of protein was considerably larger than that of carbohydrate in EPS. When the HRT decreased to 1/2 and 1/4 d, the contents of protein and carbohydrate of the second and third compartment were obviously increased, and it was 1/4 d in the first compartment. As the HRT decreased, m(protein)/m(carbohydrate) in EPS decreased, the content of EPS from cell secretion increased.(3) The study for the start-up acclimation of thermophilic ABR reactor showed that: One-step temperature rising caused failure of the ABR reactor, after 70 d operation, the COD removal efficiency was just 17%, VFAs accumulations of three compartments were 4435, 4276 and 4097 mg/L, and caused the deaths of a large number of microorganism. Mesophilic successive-step temperature rising caused successful start-up of thermophilic ABR reactor, after 50 d operation, the COD removal efficiency reached 80%, VFAs accumulations of three compartments were 3148, 1175 and 835 mg/L.(4) In the study of temperature,The operation effect of thermophilic ABR reactor was better as compared to the mesophilic reactor. The COD removal efficiency was 92% in the thermophilic reactor, while it was 86% in the mesophilic reactor. More protein could be degraded and more alkalinity could be produced at thermophilic process. The final alkalinity of three compartment in the thermophilic reactor was 2153, 3634 and 4513 mg/L, while it was 1792, 3145 and 4045 mg/L in the mesophilic reactor. VFAs accumulation was obviously lower in the thermophilic reactor, the VFAs concentration of three compartment in the thermophilic reactor was 2814, 1150 and 329 mg/L, while it was 3028, 1743 and 809 mg/L in the mesophilic reactor. In addition, methane production rate and coenzyme F420 content were higher at thermophilic process. In thermophilic reactor, methane production rate was 0.26, 0.331 and 0.336 LCH4/gCOD and coenzyme F420 content was 0.440, 0.652 and 0.781 μmol/gMLVSS. In mesophilic reactor, methane production rate was 0.251, 0.310 and 0.321 LCH4/gCOD and coenzyme F420 content was 0.393, 0.604 and 0.665 μmol/gMLVSS.