Elucidating the role of sub-thermophilic temperature and pre-hydrolyzation for effective upgrading scheme of old swine manure digesters.

Solids concentration, temperature, and digester configuration were subjected to biomethanation study to identify effective retrofitting schemes for old swine waste digesters. Batch assays were commenced to determine an appropriate scenario at 30-55 °C and total solids 1-3 %TS. Sub-thermophilic temperature (45 °C) was found desirable with an additional 11.1 % methane yield, while digestion at higher TS induced ammonium inhibition. Subsequent batch experiments lasted 72 hrs for hydrolytic-acidogenic assessment under various temperatures. Heating control at 45 °C and 55 °C for 24 hrs increased hydrolysis efficiency 4.6-5.7 folds above control but showed no significant difference (α = 0.05) between them. Limited heat supply from biogas engine dictated the continuous digestion study to operate pre-hydrolysis reactor at maximum temperature of 45 °C. The two-stage strategy demonstrated best overall performances at the sub-thermphilic combination, raising methane yield by 35.4 %. Next-Generation Sequencing indicated remarkable shifts in abundance and diversity, especially for hydrolytic organisms, which expanded from 54 to 70.2 % by sub-thermophilic temperature.

Investigating fouling deposition during combustion of hydrothermally treated palm empty fruit Bunch: Pilot-Scale study for industrial hydrothermal reactor.

Inorganic elements in palm empty fruit bunch (EFB) are problematic in boiler operation, causing slagging and fouling deposits. The first pilot-scale hydrothermal treatment (HTT) system was commenced in a palm oil mill to remove undesirable elements. Fuel properties, combustion behavior, and fouling deposition of HTT-EFB were investigated. Liquid temperatures and treatment times in the HTT system significantly altered EFB-fuel properties. At ≥ 60 °C, potassium removals of at least 78 % were achieved, generating EFB-fuel containing potassium below 0.5 %wt. Later, a series of EFB combustion experiments were conducted in a specially designed fixed-bed reactor to simulate the tube surface of industrial boilers. Fouling deposition from HTT-EFB combustion reduced to below half of untreated EFB at all HTT conditions and combustion temperatures studied. The deposit-to-fuel ratio of HTT-EFB combusted at 1,000 °C was 37.3 % lower than untreated EFB combusted at a typical EFB boiler at 800 °C. Results demonstrated great potential for HTT-EFB in industrial applications.

Upgrading industrial effluent for agricultural reuse: effects of digestate concentration and wood vinegar dosage on biosynthesis of plant growth promotor.

Emphasis on water reuse in agricultural sector receives a renewed interest to close the loop in circular economy, especially in dry and water-stressed regions. In this work, wastewater from cooperative smoked sheet rubber factory and the effluent (digestate) from its treatment system (anaerobic digester) were used as medium to grow purple non-sulfur bacteria (PNSB), Rhodopseudomonas palustris strain PP803, with wood vinegar supplement at mid-log growth phase to stimulate the release of 5-aminolevulinic acid (ALA), a plant growth promotor. Wastewater-to-digestate ratios (D:W) represented by soluble chemical oxygen demand (SCOD) were found to influence both the growth of R. palustris and synthesis of ALA. The highest ALA release of 16.02 ± 0.75 µM and the biomass accumulation of 1302 ± 78 mg/L were obtained from the medium SCOD of 4953 mg/L. Although retarding biomass accumulation by 28-36%, wood vinegar (WV) addition was proven to improve ALA release by 40%. Result suggested that SCOD of 3438 mg/L (75:25 D:W) contained sufficient carbon source for PNSB growth and was chosen to subsequently run the photo-bioreactor (PBR) to sustain R. palustris PP803 cells production. In continuous PBR operation, PNSB proliferation suffered from the low organic concentration in PBR at low organic loading. An organic loading increase to 1.21 g COD/L day was found to attain highest biomass concentration and longest PNSB dominant period over microalgea. In this study, a real-time monitoring protocol of PNSB and microalgae was specifically developed based on image color analysis at acceptable accuracy (R2 = 0.94). In the final assay, verification of the PBR-grown inoculant was conducted and ALA release efficiency was discussed under various wood vinegar dosages and dosing frequencies. This work has advanced our understandings closer to practical field application.

Effects of size and thermophilic pre-hydrolysis of banana peel during anaerobic digestion, and biomethanation potential of key tropical fruit wastes.

Methane production potential of tropical fruit wastes, namely lady-finger banana peel, rambutan waste and longan waste were compared using BMP assay and stoichiometric modified Buswell and Mueller equation. Methane yields based on volatile solid (VS) were in the order of ground banana peel, chopped banana peel, chopped longan waste, and chopped rambutan waste (330.6, 268.3, 234.6 and 193.2 mLCH4/gVS) that corresponded to their calculated biodegradability. In continuous operations of banana peel digestion at feed concentrations based on total solid (TS) 1-2%, mesophilic single stage digester run at 20-day hydraulic retention time (20-day HRT) failed at 2%TS, but successfully recovered at 1.5%TS. Pre-hydrolysis thermophilic reactor (4-d HRT) was placed as pre-treatment to mesophilic reactor (20-d HRT). Higher biogas (with an evolution of H2) and energy yields were obtained and greater system stability was achieved over the single stage digestion, particularly at higher solid feedstock. The best performance of two stage digestion was 68.5% VS destruction and energy yield of 2510.9kJ/kgVS added at a feed concentration of 2%TS.

Effects of pH adjustment by parawood ash and effluent recycle ratio on the performance of anaerobic baffled reactors treating high sulfate wastewater.

The objective of this study was to compare the performance of anaerobic baffled reactor (ABR) treating concentrated rubber latex wastewater under different pH adjustment substances and recycling ratios (R). Two ABRs, one received wastewater pretreated with NaOH and the other with ash, were operated at 35 degrees C under identical HRTs from 10 to 1.25d. Results show that both ABRs had highest COD and sulfate removal efficiencies at HRT 10d (averaged 82.71% and 96.16% of ABR-NaOH, and 80.77% and 96.60% of ABR-Ash, respectively), where majority of the influent COD and sulfate were removed by the first compartment of the ABR at all conditions tested. Increasing R (0, 0.3 and 0.5) raised the hydraulic loading on the system and resulted in a drop of organic removal efficiency and methane yield. Translocation of sulfate reducing bacteria and methanogens in the ABRs caused by increased organic loading and effluent recycle is discussed. The results show great potential of parawood ash as a pH adjustment substance for acidic wastewaters.