Xinmin Zhan

Effect of pig manure to grass silage ratio on methane production in batch anaerobic co-digestion of concentrated pig manure and grass silage

Anaerobic co-digestion of concentrated pig manure (PM) with grass silage (GS) at five different PM to GS volatile solid (VS) ratios of 1:0, 3:1, 1:1, 1:3 and 0:1 was evaluated by examining operation stability and methane (CH(4)) production potentials. The highest specific CH(4) yields were 304.2 and 302.8 ml CH(4)/g VS at PM to GS ratios of 3:1 and 1:1, respectively. The digestion systems failed at the ratio of 0:1. The lag phase lasted 29.5, 28.1, 24.6 and 21.3 days at the ratios of 1:0, 3:1, 1:1 and 1:3, respectively. The daily methane yield was linearly correlated with the acetic acid concentration, indicating methane production was probably associated with acetoclastic methanogenesis. The hydrolysis constant linearly decreased with increasing the fraction of GS in the feedstock. This study recommends applying the PM to GS ratio of 1:1 in practice due to a high specific methane yield and a short lag phase.

Mechanism of lead adsorption from aqueous solutions using an adsorbent synthesized from natural condensed tannin.

Adsorption is a method for removing lead from wastewater. The adsorption of lead on a new adsorbent synthesized from natural condensed tannin has been investigated using a series of batch adsorption experiments. The study on the adsorption mechanism indicates that the adsorbent performed in aqueous solutions as an ionic exchanger whose end group was sodium ion (Na(+)). One lead (II) ion (Pb(2+)) was adsorbed onto the adsorbent by taking the place of two Na(+) ions. The maximum exchangeable Na(+) present on the adsorbent was measured with the proton titration experiments and it was up to 1.0 mmol x Na(+)g(-1) dry adsorbent. To a significant extent, pH influenced the extraction of lead from aqueous solutions. The lead removal efficiency was up to 71%, 87% and 91% with initial solution pH at 3.0, 3.6 and 4.2, respectively. The Langmuir equation fitted the adsorption isotherm data well. The maximum adsorption capacity of lead calculated was 57.5, 76.9 and 114.9 mg lead g(-1) dry adsorbent at initial solution pH of 3.0, 3.6 and 4.2, respectively. Therefore, the adsorbent does offer favorable characteristics in lead removal from acidic wastewater.

Effects of thermo-chemical pre-treatment of grass silage on methane production by anaerobic digestion.

Dried grass silage (GS) was pre-treated at different NaOH loading rates (1%, 2.5%, 5% and 7.5% by volatile solids (VS) mass in grass silage) and temperatures (20 °C, 60 °C, 100 °C and 150 °C) to determine effects on its bio-degradability in terms of the hydrolysis yield and degradation of ligno-cellulosic materials for biogas production. At 100 °C and the four NaOH loadings, up to 45% of the total COD was solubilised and up to 65.6%, 36.1% and 21.2% of lignin, hemicellulose and cellulose were removed, respectively; biological methane production potentials obtained were 359.5, 401.8, 449.5 and 452.5 ml CH₄/g VS added, respectively, being improved by 10-38.9% in comparison with untreated GS. VS removals following anaerobic digestion were 67.6%, 76.9%, 85.3%, 95.2% and 96.7% for untreated GS and GS treated at the four NaOH loadings, respectively. 100 °C and the NaOH loading rate of 5% is recommended as a proper GS pre-treatment condition.

Methane production from anaerobic co-digestion of the separated solid fraction of pig manure with dried grass silage

Anaerobic co-digestion of the solid fraction of separated pig manure (SPM) with dried grass silage (DGS) was evaluated in three identical continuously stirred tank reactors (CSTRs) at 35±1 °C. The feedstock contained 20% DGS in CSTR1, 30% DGS in CSTR2 and 40% DGS in CSTR3 on a volatile solids (VS) basis. Organic loading rates (OLR) of 1.0, 1.5, 2.0 and 3.0 kg VS/m(3)/d were studied and it was found that the OLR affected the digester performance more than the DGS proportion in the feedstock. Tripling the OLR increased volumetric methane yields by 88% and decreased specific methane yields by 38%. At the OLR of 3 kg VS/m(3)/d, post-methane production potentials of digestates ranged from 38% to 41% of total methane production potentials of the feedstock. An energy yield estimation on a 654-sow pig unit showed that 268-371 MWh/a electricity and 383-530 MWh/a heat would be generated.

Characterization of organic matter degradation during composting of manure-straw mixtures spiked with tetracyclines.

The objective of this study was to investigate humification and mineralization of manure-straw mixtures contaminated by tetracyclines during composting. Hen manure, pig manure and rice straw were used as the raw materials. The manure-straw mixtures were spiked with tetracycline, chlortetracycline, and oxytetracycline at the concentration of 60 mg/kg dry matter. The results show that tetracyclines had no obvious influence on the composting process and more than 93% of the tetracyclines was decreased during a 45-day composting. The Fourier transform infrared (FTIR) spectra indicated that easily biodegradable components such as aliphatic substrates, carbohydrates and polysaccharides were decomposed and the contents of aromatic components relatively rose during the composting. The X-ray diffraction (XRD) spectra confirmed the natural formation of struvite, the degradation of easily biodegradable components, and the mineralization of organic matter during the composting. Therefore, FTIR and XRD analysis can be useful tools for monitoring the composting process.

Effect of the solid content on anaerobic digestion of meat and bone meal

The effect of the solid content on anaerobic digestion of meat and bone meal (MBM) was investigated in batch reactors at MBM solid contents of 1%, 2%, 5% and 10%. There was no significant difference in the specific methane (CH(4)) production potential with respect to the total volatile MBM solids (TVS) applied at these solid contents, which ranged from 351 to 381 ml CH(4)/g TVS. However, the highest CH(4) yield with respect to the removed volatile MBM solids (RVS) was 482 ml CH(4)/g RVS at the MBM solid content of 5%; the CH(4) yields were 384-448 ml CH(4)/g RVS at the other MBM solid contents. The lag time of CH(4) production rose with the increase in the solid content. The longer lag time at MBM solid contents of 5% and 10% was due to inhibition caused by high concentrations of volatile fatty acids (VFAs) and free ammonia in the reactors, but the inhibition was reversible. The production of VFAs during the digestion varied with solid contents: at the solid content of 1%, only acetic acid was detected; at 2%, both acetic and propionic acids were detected; and at 5% and 10%, acetic, propionic, butyric and valeric acids were detected. After 93-day digestion, the volatile MBM solid reduction was 92%, 91%, 79% and 80% at MBM solid contents of 1%, 2%, 5% and 10%, respectively.

Nutrient removal from slaughterhouse wastewater in an intermittently aerated sequencing batch reactor

The performance of a 10 L sequencing batch reactor (SBR) treating slaughterhouse wastewater was examined at ambient temperature. The influent wastewater comprised 4672+/-952 mg chemical oxygen demand (COD)/L, 356+/-46 mg total nitrogen (TN)/L and 29+/-10 mg total phosphorus (TP)/L. The duration of a complete cycle was 8 h and comprised four phases: fill (7 min), react (393 min), settle (30 min) and draw/idle (50 min). During the react phase, the reactor was intermittently aerated with an air supply of 0.8L/min four times at 50-min intervals, 50 min each time. At an influent organic loading rate of 1.2g COD/(Ld), average effluent concentrations of COD, TN and TP were 150 mg/L, 15 mg/L and 0.8 mg/L, respectively. This represented COD, TN and TP removals of 96%, 96% and 99%, respectively. Phase studies show that biological phosphorus uptake occurred in the first aeration period and nitrogen removal took place in the following reaction time by means of partial nitrification and denitrification. The nitrogen balance analysis indicates that denitrification and biomass synthesis contributed to 66% and 34% of TN removed, respectively.

Microbial lipid production from potato processing wastewater using oleaginous filamentous fungi Aspergillus oryzae

Use of potato processing wastewater for microbial lipid production by oleaginous filamentous fungus Aspergillus oryzae was studied with the purpose of recycling potato processing wastewater for biodiesel production. The wastewater contained high concentrations of solids, starch and nutrients. Sterilization of the potato processing wastewater resulted in a thick gelatinized medium, causing the fungi to grow slow. In order to overcome this problem, the wastewater was diluted with tap water at three dilution ratios (25%, 50% and 75% before fermentation). Dilution of the wastewater not only enhanced lipid production, starch utilization and amylase secretion but also COD and nutrient removal. The dilution ratio of 25% was found to be optimum for lipid production and the maximum lipid concentration obtained was 3.5 g/L. Lipid accumulation was influenced by amylase secretion, and the amylase activity was up to 53.5 IU/mL at 25% dilution. The results show that phosphate limitation may be the mechanism to stimulate the lipid accumulation. In addition to lipid production, removals of COD, total soluble nitrogen and total soluble phosphorus up to 91%, 98% and 97% were achieved, respectively. Microbial lipids of A. oryzae contained major fatty acids such as palmitic acid (11.6%), palmitolic acid (15.6%), stearic acid (19.3%), oleic acid (30.3%), linolenic acid (5.5%) and linoleic acid (6.5%) suggesting that the lipids be suitable for second generation biodiesel production.

Economic analyses of pig manure treatment options in Ireland

An economic analysis was performed on treatment options for pig manure in Ireland. Costs were based on a 500 sow integrated pig farm producing 10,500 m(3) of manure per year at 4.8% dry matter. The anaerobic digestion of pig manure and grass silage (1:1; volatile solids basis) was unviable under the proposed tariffs, with costs at € 5.2 m(-3) manure. Subsequent solid-liquid separation of the digestate would cost an additional € 12.8 m(-3) manure. The treatment of the separated solid fraction by composting and of the liquid fraction by integrated constructed wetlands, would add € 2.8 and € 4.6 m(-3) manure, respectively to the treatment costs. The cost analysis presented showed that the technologies investigated are currently not cost effective in Ireland. Transport and spreading of raw manure, at € 4.9 m(-3) manure (15 km maximum distance from farm) is the most cost effective option.

Nitrous oxide emission and nutrient removal in aerobic granular sludge sequencing batch reactors

Application of aerobic granular sludge into wastewater treatment is promising due to its excellent settling ability and high microbial concentrations. However, its spatial structure could induce incomplete denitrification, leading to generation of nitrous oxide (N(2)O) - a potent greenhouse gas. Under the temperature of 14 ± 4 °C, three identical laboratory-scale aerobic granular sludge sequencing batch reactors (SBRs) were established to treat synthetic wastewater simulating a mixture of liquid pig manure digestate and municipal wastewater at three aeration rates (0.2, 0.6 and 1.0 L air/min) and three COD:N ratios (1:0.22, 1:0.15 and 1:0.11). The studies show the proportions of N(2)O emission to the influent nitrogen loading rate at the aeration rates of 0.2, 0.6 and 1.0 L air/min were 8.2%, 6.1% and 3.8% at a COD:N ratio of 1:0.22; 7.0%, 5.1% and 3.5% at a COD:N ratio of 1:0.15; and 4.4%, 2.9% and 2.2% at a COD:N ratio of 1:0.11, respectively. With NO(2)(-) as the only nitrogen source in the liquid phase, the specific N(2)O generation rates via denitrification were 1.7, 1.6 and 1.3 μg N(2)O/(g SS· min) at the aeration rates of 0.2, 0.6 and 1.0 L air/min, respectively, which were 40.9%, 44.8%, 39.9% higher than those with NO(3)(-) as the only nitrogen source, respectively. N(2)O generation by aerobic granular sludge due to NH(4)(+)-N nitrification was not sensitive to the aeration rate, and the average specific N(2)O generation rate was 0.8 ± 0.02 μg N(2)O/(g SS· min).