Impact of roxarsone on the UASB reactor performance and its degradation

Roxarsone （3-nitro-4-hydroxyphenylarsonic acid, ROX） has been widely used for decades as an organoarsenic feed additive to control intestinal parasites and improve feed efficiency in animal production. However, most of the ROX is excreted into the manure, causing arsenic contamination in wastewater. The arsenic compounds are toxic to microorganisms, but the influence of continuous ROX loading on upflow anaerobic sludge blanket （UASB） reactor is still unknown. In this study, the impact of ROX and its degradation products on the performance of the UASB reactor and the degradation and speciation of ROX in the reactor were investigated. The UASB reactor （hydraulic retention time： 1.75 d） was operated using synthetic wastewater supplemented with ROX for a period of 260 days. With continuous ROX addition at 25.0 mg.L-1, severe inhibition to methanogenic activity occurred after 87 days operation accompanied with an accumulation of volatile fatty acids （VFAs） and a decline in pH. The decrease of added ROX concentration to 13.2 mg.L-1 did not mediate the inhibition. As（III）, As （V）, MMA（V）, DMA（V）, HAPA and an unknown arsenic compound were detected in the reactor, and a possible biotransformation pathway of ROX was proposed. Mass balance analysis of arsenic indicated that 60%-70% of the arsenic was discharged into the effluent, and 30%-40% was precipitated in the reactor. The results from this study suggest that we need to pay attention to the stability in the UASB reactors treating organoarsenic-contaminated manure and wastewater, and the effluent and sludge from the reactor tO avoid diffusion of arsenic contamination.

Aggravation of membrane fouling and methane leakage by a three-phase separator in an external anaerobic ceramic membrane bioreactor

The three-phase separator is a critical component of high-rate anaerobic bioreactors due to its significant contribution in separation of biomass, wastewater, and biogas. However, its role in an anaerobic membrane bioreactor is still not clear. In this study, the distinction between an external anaerobic ceramic membrane bioreactor (EAnCMBR) unequipped (R1) and equipped (R2) with a three-phase separator was investigated in terms of treatment performance, membrane fouling, extracellular polymers of sludge, and microbial community structure. The results indicate that the COD removal efficiencies of Rl and R2 were 98.2%±0.4% and 98.1%±0.4%, respectively, but the start-up period of R2 was slightly delayed. Moreover, the membrane fouling rate of R2 (0.4 kPa/d) was higher than that of Rl (0.2 kPa/d). Interestingly, the methane leakage from R2 (0.1 L/d) was 20 times higher than that from Rl (0.005 L/d). The results demonstrate that the three-phase separator aggravated the membrane fouling rate and methane leakage in the EAnCMBR. Therefore, this study provides a novel perspective on the effects of a three-phase separator in an EAnCMBR.

Influence of arsanilic acid, Cu2＋, PO43- and their interaction on anaerobic digestion of pig manure

Arsanilic acid （ASA）, copper ion （Cuz ＋） and phosphate （PO43 ） are widely used as feed additives for pigs. Most of these three supplemented feed additives were excreted in feces and urine Anaerobic 2＋ digestion is often used for the management of pig manure. However the interaction ofASA with Cu 3 ＇ 2＋ 3 or P04 on anaerobic ＆gestlon is still not clear. In thin study, the influence ofASA, Cu , PO4- and their interaction on anaerobic digestion of pig manure and the possible mechanisms were investigated. The initial concentrations ofASA, Cu2＋ and PO43 were 0.46 mM, 2 mM and 2 mM in the anaerobic digester, respectively. The methanogenesis was severely inhibited in the assays with only ASA addition, only Cu2＋ addition and ASA ＋ PO43 addition with the inhibition index of 97.8%, 46.6% 2＋ and 82.6%, respectively, but the methanogenesis inhibition in the assay with ASA ＋ Cu addlt on was mitigated with the inhibition index of 39.4%. PO43 had no obvious impacts on the degradation of ASA. However, Cu2＋ addition inhibited the degradation of ASA, and mitigated the methanogcnesis inhibition. The existence of ASA would inhibit methanogenesis and generate more toxic inorganic arsenic compounds during anaerobic digestion, implying the limitation of anaerobic digestion for ASA- contaminated animal manure. However, the co-existence of ASA and Cu2＋ could mitigate the inhibition. These results could provide useful information for the management of anaerobic digestion of pig manure containing ASA and Cu2＋ .

Thermochemical pretreatment of meat and bone meal and its effect on methane production

Since the solubilization of meat and bone meal(MBM)is a prerequisite in many MBM disposal approaches,enhancement of the solubilization by means of thermochemical pretreatment was investigated in this study at two temperatures(55℃and 131℃)and six sodium hydroxide(NaOH)concentrations(0,1.25,2.5,5,10 and 20 g/L).The MBM volatile solid(VS)reduction ratio was up to 66%and 70%at 55℃and 131℃,respectively.At the same temperature,the VS reduction ratio increased with the increase in the dosage of NaOH.The study on the methane(CH4)production potential of pretreated MBM shows that the addition of NaOH at 55℃did not cause the inhibition of the succeeding CH4 production process.However,CH4 production was inhibited by the addition of NaOH at 131℃.The CH4 production potential was in the range of 389 to 503 mL CH4/g VS MBM and 464 to 555 mL CH4/g VS MBM at 55℃and 131℃,respectively.