- Water science and technology : a journal of the International Association on Water Pollution Research
- Published over 6 years ago
This study aims to investigate solubilization of elements (P, N, K, Ca and Mg) during anaerobic digestion (AD) of solid agriculture waste. It is important to maintain particularly phosphorous in the aqueous phase to be able to subsequently recover it in a concentrated form via crystallization. Batch AD was carried out at a mesophilic condition (37 °C) and pH 7.0 ± 0.2 on a variety of piggery and poultry solid waste streams. Less than 10% of the total P, Ca and Mg was in soluble form in the digestate. Most of the N and K remained soluble in the digestate. A bioavailability test (citric acid extraction) showed P, Ca and Mg in the digestate were totally available. Complete solubilization of P, Ca and Mg occurred below a threshold of pH 5.5. This indicates these nutrients were released during digestion, and then either bound to form inorganic compounds or adsorbed on solid surfaces in the digestate. These effects reduce the feasibility of post-digestion recovery of the nutrients via struvite crystallization. Strategies to improve nutrient solubilization and recovery during the AD include addition of complexing chemicals, operation at depressed pH, or otherwise modifying the operating conditions.
Solid-state anaerobic digestion (SS-AD) and composting of yard trimmings with effluent from liquid AD were compared under thermophilic condition. Total solids (TS) contents of 22%, 25%, and 30% were studied for SS-AD, and 35%, 45%, and 55% for composting. Feedstock/effluent (F/E) ratios of 2, 3, 4, 5, and 6 were tested. In composting, the greatest carbon loss was obtained at 35% TS, which was 2-3 times of that at 55% TS and was up to 50% higher than that in SS-AD. In SS-AD, over half of the degraded carbon was converted to methane with the greatest methane yield of 121 L/kg VS(feedstock). Methane production from SS-AD was low at F/E ratios of 2 and 3, likely due to the inhibitory effect of high concentrations of ammonia nitrogen (up to 5.6g/kg). The N-P-K values were similar for SS-AD digestate and compost with different dominant nitrogen forms.
To enhance the treatment efficiency from an anaerobic digester, a novel six-compartment anaerobic/oxic baffled reactor (A/OBR) was employed. Two kinds of split-feeding A/OBRs R2 and R3, with influent fed in the 1(st), 3(rd) and 5(th) compartment of the reactor simultaneously at the respective ratios of 6:3:1 and 6:2:2, were compared with the regular-feeding reactor R1 when all influent was fed in the 1(st) compartment (control). Three aspects, the COD removal, the hydraulic characteristics and the bacterial community, were systematically investigated, compared and evaluated. The results indicated that R2 and R3 had similar tolerance to loading shock, but the R2 had the highest COD removal of 91.6% with a final effluent of 345 mg/L. The mixing patterns in both split-feeding reactors were intermediate between plug-flow and completely-mixed, with dead spaces between 8.17% and 8.35% compared with a 31.9% dead space in R1. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed that the split-feeding strategy provided a higher bacterial diversity and more stable bacterial community than that in the regular-feeding strategy. Further analysis indicated that Firmicutes, Bacteroidetes, and Proteobacteria were the dominant bacteria, among which Firmicutes and Bacteroidetes might be responsible for organic matter degradation and Proteobacteria for nitrification and denitrification.
Anaerobic digestion of aqueous pyrolysis liquor derived from pyrolysis of solid digestate was tested in batch mode using an un-adapted inoculum. Three pyrolysis liquors produced at 330°C, 430°C and 530°C in four COD-based concentrations of 3, 6, 12 and 30gL(-1) were investigated. The three lower concentrations showed considerable biogas production, whereas the 30gL(-1) dosage caused process inhibition. The highest methane yield of 199.1±18.5mLgCOD(-1) (COD removal: 56.9±5.3%) was observed for the 330°C pyrolysis liquor, followed by the 430°C sample with only slightly lower values. The 530°C sample dropped to a yield of 129.3±19.7mLgCOD(-1) (COD removal: 36.9±5.6%). Most VOCs contained in the pyrolysis liquor (i.e. furfural, phenol, catechol, guaiacol, and levoglucosan) were reduced below detection limit (cresol by 10-60%). Consequently, integrated pyrolysis and anaerobic digestion in addition to thermochemical conversion of digestate also promises bioconversion of pyrolysis liquors.
Triclocarban (TCC) is one of the most abundant organic micropollutants detected in biosolids. Lab-scale anaerobic digesters were amended with TCC at concentrations ranging from the background concentration of seed biosolids (30 mg/kg) to toxic concentrations of 850 mg/kg to determine the effect on methane production, relative abundance of antibiotic resistance genes, and microbial community structure. Additionally, the TCC addition rate was varied to determine the impacts of acclimation time. At environmentally relevant TCC concentrations (max detect = 440 mg/kg) digesters maintained function. Digesters receiving 450 mg/kg of TCC maintained function under gradual TCC addition, but volatile fatty acid concentrations increased, pH decreased, and methane production ceased when immediately fed this concentration. The concentrations of the mexB gene (encoding for a multidrug efflux pump) were higher with all concentrations of TCC compared to a control, but higher TCC concentrations did not correlate with increased mexB abundance. The relative abundance of the gene tet(L) was greater in the digesters that no longer produced methane, and no effect on the relative abundance of the class 1 integron integrase encoding gene (intI1) was observed. Illumina sequencing revealed substantial community shifts in digesters that functionally failed from increased levels of TCC. More subtle, yet significant, community shifts were observed in digesters amended with TCC levels that did not inhibit function. This research demonstrates that TCC can select for a multidrug resistance encoding gene in mixed community anaerobic environments, and this selection occurs at concentrations (30 mg/kg) that can be found in full-scale anaerobic digesters (US median concentration = 22 mg/kg, mean = 39 mg/kg).
Lignocellulosic biomass is one of the most abundant yet underutilized renewable energy resources. Both anaerobic digestion (AD) and hydrothermal carbonization (HTC) are promising technologies for bioenergy production from biomass in terms of biogas and HTC biochar, respectively. In this study, the combination of AD and HTC is proposed to increase overall bioenergy production. Wheat straw was anaerobically digested in a novel upflow anaerobic solid state reactor (UASS) in both mesophilic (37 °C) and thermophilic (55 °C) conditions. Wet digested from thermophilic AD was hydrothermally carbonized at 230 °C for 6 hr for HTC biochar production. At thermophilic temperature, the UASS system yields an average of 165 LCH4/kgVS (VS: volatile solids) and 121 L CH4/kgVS at mesophilic AD over the continuous operation of 200 days. Meanwhile, 43.4 g of HTC biochar with 29.6 MJ/kgdry_biochar was obtained from HTC of 1 kg digestate (dry basis) from mesophilic AD. The combination of AD and HTC, in this particular set of experiment yield 13.2 MJ of energy per 1 kg of dry wheat straw, which is at least 20% higher than HTC alone and 60.2% higher than AD only.
Methane production by the anaerobic digestion of seaweed is restricted by the slow degradation caused by the influence of the rigid algal cell wall. At the present time, there has been no study focusing on the anaerobic digestion of U. lactuca by co-fermentation and pre-treatment with rumen fluid. Rumen fluid can favor methane production from algal biomass by utilizing the diversity and quantity of bacterial and archaeal communities in the rumen fluid. This research presents a novel method based on combined ADS and rumen fluid pre-treatment to improve the production of methane from seaweed. Biochemical methane potential (BMP) tests were performed to investigate the biogas production using combined ADS and rumen fluid pre-treatment at varied inoculum ratios on the performance of methane production from U. lactuca biomass. Compared to the control (no rumen fluid pre-treatment), the highest BMP yields of U. lactuca increased from 3%, 27.5% and 39.5% to 31.1%, 73% and 85.6%, respectively, for three different types of treatment. Microbial community analysis revealed that the Methanobrevibacter species, known to accept electrons to form methane, were only detected when rumen fluid was added. Together with the significant increase in species of Methanoculleus, Methanospirillum and Methanosaeta, rumen fluid improved the fermentation and degradation of the microalgae biomass not only by pre-treatment to foster cell-wall degradation but also by relying on methane production within itself during anaerobic processes. Batch experiments further indicated that rumen fluid applied to the co-fermentation and pre-treatment could increase the economic value and hold promise for enhancing biogas production from different seaweed species.
Effects of activated carbon (AC) supplementation on anaerobic digestion (AD) of food waste were elucidated in lab- and pilot-scales. Lab-scale AD was performed in 1 L and 8 L digesters, while pilot-scale AD was conducted in a 1000 L digester. Based on the optimal dose of 15 g AC per working volume derived from the 1 L digester, for the same AC dosage in the 8 L digester, an improved operation stability coupled with a higher methane yield was achieved even when digesters without AC supplementation failed after 59 days due to accumulation of substantial organic intermediates. At the same time, color removal from the liquid phase of the digestate was dramatically enhanced and the particle size of the digestate solids was increased by 53% through AC supplementation after running for 59 days. Pyrosequencing of 16S rRNA gene showed the abundance of predominant phyla Firmicutes, Elusimicrobia and Proteobacteria selectively enhanced by 1.7-fold, 2.9-fold and 2.1-fold, respectively. Pilot-scale digester without AC gave an average methane yield of 0.466 L⋅(gVS)-1⋅d-1at a composition of 53-61% v/v methane. With AC augmentation, an increase of 41% in methane yield was achieved in the 1000 L digester under optimal organic loading rate (1.6 g VSFW·L-1·d-1).
Degradation and solid-liquid distribution of antibiotics in three sludge pretreatments (ultrasonic, alkaline and thermal hydrolysis pretreatment) and subsequent anaerobic digestion processes were investigated. The contamination of fluoroquinolones (FQs) was most serious in the raw sludge, while sulfonamides (SAs) were negligible. Obvious solubilization of antibiotics was observed after sludge pretreatments. The intracellular antibiotics were released after thermal hydrolysis pretreatment, meanwhile tetracyclines (TCs) were thermally decomposed. Compared to TCs and macrolides (MLs), FQs were hardly degraded in anaerobic digestion with removal efficiencies lower than 42.02%, and the residual FQs were mostly adsorbed on the digested sludge. The limiting step for FQs reduction was the biodegradation, rather than desorption of adsorbed antibiotics. Addition of pretreatments had no obvious effect on the degradation and distribution of antibiotics in the anaerobic digested sludge, except that the thermal hydrolysis enhanced the migration of antibiotics to the liquid phase.
The primary objective of this research was to remove recalcitrant nutrients from anaerobically digested sludge dewatering centrate. A struvite precipitation methodology is proposed where salt crystals are encouraged to ballast colloidal particles through heterogeneous nucleation and subsequent crystal growth. The secondary objective was to assess presence of micropollutants in precipitates. Four biologically unique dewatering centrates were used to test the precipitation methodology on the variety of anaerobic digester configurations that can be expected from municipal wastewater treatment plant. The effect of digestion sludge retention time (2 day, 20 day) and digestion temperature (35 °C, 55 °C) on the removal of dissolved unreactive phosphorus (P) and nitrogen (N) was monitored. Averaged across all four centrates, the precipitation methodology resulted in dissolved unreactive P and N removal of 82.4% and 66.6%, respectively. Antimicrobial contaminants (triclosan, triclocarban) were observed in the precipitates at minute concentrations (<18 ng/g-dry solids). Therefore, mass struvite precipitation can provide a means of recalcitrant nutrient treatment and reactive nutrient recovery without the micropollutant burden of biosolids land application.