Volatile Solids Removal Rate Research Articles

Effect of Volatile Fatty Acid Concentration on Anaerobic Degradation Rate from Field Anaerobic Digestion Facilities Treating Food Waste Leachate in South Korea

The purpose of this study was to investigate the effect of volatile fatty acid concentration on anaerobic degradation rate of food waste leachate in the anaerobic digestion facilities. The anaerobic digestion facilities treating food waste leachate (FWL), codigestion with food leachate and animal manure (A-MIX), and codigestion with food waste leachate and sewage sludge (S-MIX) were selected for this study. In accordance with the regulation under Wastes Control Act in South Korea, the guideline of volatile solid removal rate for anaerobic digestion facility is set as 65% for anaerobic degradation efficiency. Highest volatile solids removal rates were achieved from FWL (63.5%) than A-MIX (56.4%) and S-MIX (41.2%). Four out of eight FWLs met the guidelines. The concentration of volatile fatty acids, therefore, was analyzed to determine the relationship with volatile solid removal rate. The results showed that, in order to meet the Korean guideline of 65% volatile solid removal rate, volatile fatty acid concentrations should remain below 4,000 mg/L on the field anaerobic digestion facilities treating FWL. Volatile fatty acid concentrations should be used along with others as an operational parameter to control and manage the anaerobic digestion process.

Industrial sludge remediation with photonic treatment using Ti–Ag nano-composite thin films: Persistent organic pollutant removal from sludge matrix

Mechanically dewatered industrial sludge (MDIS) was treated using pure and silver-doped thin films (TFs) grown on quartz substrates. TFs were prepared using a sol–gel dip coating technique. The resulting films were annealed at 450 °C for 3 h and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Mixtures that were homogeneous in the UV A (380 nm) and UVvis (450 nm) regions of the electromagnetic spectrum were used as the irradiation source. The results revealed that illumination with different wavelengths helps to generate well-separated e−/h+ pairs, resulting in a decrease in the recombination rate. An electron transfer chain model was also developed using the experimental results. The performance of the applied method was evaluated by observing variations in the sludge bound water content (SBWC), volatile solids removal rate (VSR), and the consumed and generated energy fluxes through endergonic and exergonic reactions. After treatment, SBWC was reduced from 65% ± 1% to 39% ±1 and the highest VSR was measured to be 27 ± 0.1 mg VSS cm−2 h−1. The consumed and recovered energy fluxes were 960 ± 151 and 412 ± 26 J g−1 VSremoved, respectively. Raw sludge and polychlorinated biphenyls (∑15PCB) and polyaromatic hydrocarbon (∑16PAH) concentrations were 4356.82 ± 22 μg kg−1 and 446.25 ± 4.8 μg kg−1, respectively. The ∑15PCB and ∑16PAH concentrations in the treated sludge samples were 129.86 ± 22 μg kg−1 and 34.85 ± 1.3 μg kg−1, respectively.

Evaluation of batch anaerobic co-digestion of palm pressed fiber and cattle manure under mesophilic conditions

Palm pressed fiber (PPF) and cattle manure (CM) are the waste which can be managed properly by anaerobic co-digestion. The biogas production in co-digested PPF and CM at three volatile solids (VS) ratios of 3:1, 1:1, and 1:3 was investigated in a series of batch experiments at an organic loading rate of 30.0g VS/L under mesophilic (37±1°C) conditions. The highest daily biogas yield of PPF and CM only, was 90.0mL/g VSadded at day 12 and 23.4mL/g VSadded at day 7. For co-digestion of PPF/CM at mixing ratios of 3:1, 1:1 and 1:3, there were 93.6mL/g VSadded at day 11, 86.8 and 26.4mL/g VSadded at day 8. VS removal rate for PPF, CM, and co-digestion at mixing ratio of 3:1, 1:1, and 1:3 were 91.1%, 86.0% and 71.0%, respectively. The anaerobic digestion of PPF and CM and their co-digestion systems were stable in operation with low range of volatile fatty acids (VFA)/TIC (total inorganic carbon) of (0.035–0.091). The main volatile fatty acids were propionic, and iso-butyric acids for PPF, iso-butyric and n-butyric acids for CM. The VFAs and ammonium inhibition were not occurred. The modified Gompertz model can be used to perform a better prediction with a lower difference between the measured and predicted biogas yields. A VS ratio of 3:1 is recommended for practice.

Evaluation of thermal, thermal-alkaline, alkaline and electrochemical pretreatments on sludge to enhance anaerobic biogas production

Anaerobic digestion was regarded as one of the ways to recover energy from waste activated sludge in this study. After applying thermal-, thermal-alkaline-, electrochemical- and alkaline-pretreatments to waste activated sludge to promote the digestion efficiency, biogas yield and volatile solid (VS) removal were investigated to evaluate the effectiveness of the pretreatments for the purpose. The highest biogas production (647L/kg VS) was achieved after pretreatment by electrochemical method. The highest daily biogas production rate was obtained through alkaline pretreatment. Biogas production has no positive relationship with the solubilization degree of sludge. The highest VS removal rate could be got by the pretreatment of thermo-alkaline and electrochemical methods, and the sludge achieved the stabilization after the shortest digestion time with the treatment of electrochemical.

Combined Mesophilic Anaerobic and Thermophilic Aerobic Digestion Process: Effect on Sludge Degradation and Variation of Sludge Property

One-stage autothermal thermophilic aerobic digestion (ATAD) is effective for the reduction of volatile solids (VSs) and pathogen in sewage sludges. A novel process of combining mesophilic (<35 °C) anaerobic digestion with a thermophilic (55 °C) aerobic digestion process (AN/TAD) occurred in a one-stage digester, which was designed for aeration energy savings. The efficiency of sludge degradation and variation of sludge properties by batch experiments were evaluated for the AN/TAD digester with an effective volume of 23 L for 30 days compared with conventional thermophilic aerobic digestion (TAD). The AN/TAD system can efficiently achieve sludge stabilization on the 16th day with a VS removal rate of 38.1 %. The AN/TAD system was operated at lower ORP values in a digestion period with higher contents of total organic compounds, volatile fatty acids, protein, and polysaccharide in the soluble phase than those of the TAD system, which can rapidly decreased and had low values in the late period of digestion for the AN/TAD system. In the AN/TAD system, intracellular substances had lysis because of initial hydrolytic acidification.

DIGESTÃO ANAERÓBIA DE LODO DE ESGOTO UTILIZANDO REATORES SEQUENCIAIS: PARTIDA E ESTABILIZAÇÃO DOS SISTEMAS

The objective of this work was the implantation and evaluation of three sludge anaerobic digestionsystems. The system A configuration was defined by five continuous flow sequential anaerobicreactors (SAR) with effluent recycling. System B had the same layout, but recirculation wassubstituted by mechanical mixers installed in each reactor. System C was composed by only onecontinuous flow stirred tank reactor. The systems were evaluated by weekly monitoring of physical-chemical parameters. Samples were taken from influent, effluent and intermediary ports during anoperation period of 115 days. During the most stable operational period (PHASE II), the resultsindicated total solids removal rate of 95, 40 and 29%, and volatile solids removal rate of 95, 34 and22%, for System A, B and C, respectively. The sequential anaerobic reactors (System A and B)presented better performance than conventional digestor (System C).

Effect of Hydraulic Retention Time on the Efficiency of Vertical Tubular Anaerobic Sludge Digester Treating Waste Activated Sludge

Treating waste activated sludge at a temperature of 35 °C was investigated in vertical tubular anaerobic sludge digester and common anaerobic sludge digester, with the working volume of 2.5 m3 each. Compared with common anaerobic sludge digester, the vertical tubular anaerobic sludge digester greatly improved volatile solids and COD removal efficiencies, the methane production and the stability of the anaerobic digestion system under the same condition of hydraulic retention time. The minimum hydraulic retention time of the vertical tubular anaerobic sludge digester was 5 days, when the organic loading remained at 5.28 kg m-3 d-1 (as volatile solids) and the volatile solids removal rate was 41.7%. The suitable hydraulic retention time for vertical tubular anaerobic sludge digester was 5 days, while to get the same COD removal rate it was 10 days for common anaerobic sludge digester. At optimum hydraulic retention time of 5 days, the methane production of the two digesters achieved the maximum difference of 0.06 l g-1 volatile solids (0.26, 0.20 l g-1 volatile solids for vertical tubular anaerobic sludge digester and common anaerobic sludge digester, respectively). The advantage of vertical tubular anaerobic sludge digester was especially obvious when the hydraulic retention time was relatively short. Furthermore, it was found that the vertical tubular anaerobic sludge digester in which more anaerobic bacteria lived has significantly intensified the sub-micro mass transfer between the substrate and the microorganisms, which resulted in a remarkable effect on shortening the hydraulic retention time of anaerobic sludge digestion.

Assessment of kinetic parameters for the mesophilic anaerobic biodegradation of two-phase olive pomace

A kinetic study of the anaerobic biodegradation of two-phase olive pomace (TPOP) was carried out using a laboratory-scale stirred tank reactor. The reactor was operated at 35°C. The influent contained between 20% and 100% TPOP, representing in terms of total chemical oxygen demand (TCOD) 34.5–187.9gTCODl−1. The hydraulic retention times (HRTs) were set between 40.0 and 8.3d. It was found that the increase of influent substrate concentration favoured the process failure reducing the pH and increasing the ratio of the total volatile fatty acid (TVFA) to alkalinity. This ratio was found to be proportional to the substrate concentration (S), as follows: TVFA/alkalinity=0.04(S). The kinetic model of Andrews was used to describe the relation between anaerobic biodegradation of TCOD and Volatile Solids (VS) and the formation of methane. The values of the kinetic constants for TCOD removal were determined to be 28gTCODl−1d−1, 27gTCODl−1 and 352gTCODl−1, respectively, for maximum substrate utilization rates (RSmax), saturation constant (KS) and inhibition constant (Ki). Process inhibition started at substrate concentrations of around 20gTCODl−1. For VS biodegradation the kinetic constant values, RSmax, KS and Ki, were 45gVSl−1d−1, 37 and 36gVSl−1, respectively. Inhibition started at VS concentration of around 18gl−1. The rates of TCOD removal were lower than those observed for VS removal and inhibition of VS removal occurred at a lower concentration compared to that for TCOD. The QM(max), KS and Ki constants for methane production were approximately 3.1lCH4l−1 reactord−1, 8.7gTCODl−1 and 272gTCODl−1, respectively. Inhibition of methane formation started at a substrate concentration of around 17gTCODl−1. TCOD and VS removal rates were higher than the rate of methane formation and these differences increased when the substrate concentration increased. This fact was underlined by the decrease of pH, the increase of TVFA/alkalinity ratio and the reduction of methane production rate.