Thermal-alkaline Pretreatment Research Articles

Characterization and application of bioflocculant prepared by Rhodococcus erythropolis using sludge and livestock wastewater as cheap culture media

A new bioflocculant was produced by culturing Rhodococcus erythropolis in a cheap medium. When culture pH was 7.0, inoculum size was 2 % (v/v), Na2HPO4 concentration was 0.5 g L(-1), and the ratio of sludge/livestock wastewater was 7:1 (v/v), a maximum flocculating rate of 87.6 % could be achieved. Among 13 different kinds of pretreatments for sludge, the optimal one was the thermal-alkaline pretreatment. Different from a bioflocculant produced in a standard medium, this bioflocculant was effective over a wide pH range from 2 to 12 with flocculating rates higher than 98 %. Approximately, 1.6 g L(-1) of crude bioflocculant could be harvested using cold ethanol for extraction. This bioflocculant showed color removal rates up to 80 % when applied to direct and disperse dye solutions, but only 23.0 % for reactive dye solutions. Infrared spectrum showed that the bioflocculant contained functional groups such as -OH, -NH2, and -CONH2. Components in the bioflocculant consisted of 91.2 % of polysaccharides, 7.6 % of proteins, and 1.2 % of DNA. When the bioflocculant and copper sulfate (CuSO4) were used together for decolorization in actual dye wastewater, the optimum decolorization conditions were specified by the response surface methodology as pH 11, bioflocculant dosage of 40 mg/L, and CuSO4 80 mg/L, under which a decolorization rate of 93.9 % could be reached.

Enhancement of anaerobic digestion of waste activated sludge by electrochemical pretreatment

Electrochemical pretreatment (EP) with a pair of Ti/RuO2 mesh plate electrodes was applied to solubilize waste activated sludge (WAS) with the aid of hypochlorite, and the conventional pretreatment methods of thermal pretreatment (THP), thermal-alkaline pretreatment (TAP) and alkaline pretreatment (AP) were also introduced as the comparative cases. In this study, Growth Rate of Solubilization (GRS) was developed to characterize the solubilization process of WAS in terms of SCOD (soluble chemical oxygen demand), carbohydrates, proteins, VFAs, and the highest GRS−SCOD was found in EP-group, with approximately 5.2 times higher than that in AP group. Around 647L/kgVS (volatile solids) of biogas was obtained in EP-group, which was up to 63.4% more than that in the control group (396L/kgVS), and the corresponding VS removal efficiency reached to 45.5%. Therefore, EP might be a promising enhancement method for sludge solubilization, and thus contribute to the anaerobic digestion process.

Sequential sludge digestion after diverse pre-treatment conditions: sludge removal, methane production and microbial community changes.

A lab-scale sequential sludge digestion process which consists of a mesophilic anaerobic digester (MAD) and a thermophilic aerobic digester (TAD) was developed. Thermal, thermal-alkaline and long-term alkaline pre-treatments were applied to the feed sludge to examine their effects on sludge removal and methane production. Especially after thermal-alkaline pre-treatment, high COD removal was maintained; methane production rate was also drastically increased by improving the hydrolysis step of sludge degradation. Polymerase chain reaction-denaturing gel gradient electrophoresis indicated that bacterial communities were represented by three phyla (Firmicutes, Proteobacteria, Actinobacteria) and that Clostridium straminisolvens was the major bacterial species in MAD. Quantitative real-time PCR results indicated that Methanosaeta concilli was the major archaeal species in MAD, and that Ureibacillus sp. was the most abundant bacterial species in TAD.

Effect of thermal–alkaline pretreatment on the anaerobic digestion of streptomycin bacterial residues for methane production

The anaerobic digestion of streptomycin bacterial residues, solutions with hazardous waste treatments and bioenergy recovery, was tested in laboratory-scale digesters at 35°C at various organic loading rates (OLRs). The methane production and biomass digestion were efficient at OLRs below 2.33 gVS L(-1) d(-1) but were deteriorated as OLR increased because of the increased total ammonia nitrogen (TAN) concentration from cell protein decay. The thermal-alkaline pretreatment with 0.10 NaOH/TS at 70°C for 2 h significantly improved the digestion performance. With the thermal-alkaline pretreatment, the volumetric reactor productivity and specific methane yield of the pretreated streptomycin bacterial residue increased by 22.08-27.08% compared with those of the unpretreated streptomycin bacterial residue at an OLR of 2.33 gVS L(-1) d(-1). The volatile solid removal was 64.09%, with less accumulation of TAN and total volatile fatty acid.

Thermal-Alkaline Pretreatment on the Decomposition of the Streptomycin Bacterial Residue

ABSTRACTThere is still insufficient practical experience in the removing and degrading of streptomycin bacterial residues. The effect of thermal-alkaline pre-treatment on the decomposition of a streptomycin bacterial residue was investigated. Without NaOH pretreatment, the effect of thermal pre-treatment was not obvious. Soluble chemical oxygen demand and volatile suspended solids were 66.39% and 55.0% at 0.10 NaOH/TS ratio (g/g) and 368.15 K, respectively. The methane yield was 380 mL CH4/gVSadded at 303.15 K and no added NaOH and increased to 434 mL CH4/gVSadded at 0.10 NaOH/TS ratio (g/g) and 368.15 K. Thermal-alkaline pretreatment could significantly enhance not only the SCOD and VSS solubilization, but also the biodegradability. Methane production was enhanced, probably as a result of the breakdown of cell walls and membranes of microorganisms by thermal-alkaline pretreatment, which may facilitate the contact between organic molecules and anaerobic microorganisms.

Effect of thermal alkaline pretreatment on the anaerobic digestion of wasted activated sludge

The effect of alkaline pretreatment of waste-activated sludge, using two models to study the sequential hydrolysis rates of suspended (Sanders' surface model) and dissolved (Goel's saturation model) solids, on the mesophilic and thermophilic anaerobic digestion rate is evaluated. The pretreatment, which reduces the size of the solids, increases the reaction rate by increasing the surface area and the specific surface hydrolysis constant (K(SBK)); at thermophilic conditions from 0.45 x 10(-3) kg m(-2) d(-1) for the fresh sludge to 0.74 x 10(-3) kg m(-2) d(-1) for the pretreated sludge and at mesophilic conditions these values are 0.28 x 10(-3) kg m(-2) d(-1) and 0.47 x 10(-3) kg m(-2) d(-1) confirming the usefulness of a pretreatment for solids reduction. But for soluble solids, the thermoalkaline pretreatment decreases the reaction rates by inducing a competitive inhibition on the thermophilic anaerobic digestion rate while in the mesophilic range, a non-competitive inhibition is observed. A mathematical simulation of the consecutive reactions, suspended solids to dissolved solids and to methane in staged anaerobic thermophilic-mesophilic digestion, shows that with 4% suspended solids concentration it is better not to use a thermoalkaline pretreatment because overall solids reduction and total methane production are not as good as without pretreatment.

Pre-Treatment of Wastewater Sludge – Biodegradability and Rheology Study

This study investigates the changes in biodegradability, rheology and metal concentration of wastewater sludge – nonhydrolyzed (raw), sterilized, and hydrolyzed (thermal alkaline pre-treatment) at total solids concentration from 10-50 g l−1 to ascertain the bioavailability of nutrients for subsequent fermentation. The dissolved solids concentration increased linearly with total solids. Irrespective of the wastewater sludge (raw or, pre-treated), percentage biodegradability in terms of total solids (26.5-44.5%), total COD (25.8-56.5%) and dissolved solids (41.9-66.9%) was maximum around 20 g l−1 solids concentration. The pseudoplasticity of sludge decreased (consistency index decreased from 895.1 to 5.2 and flow behaviour index increased from 0.28 to 0.88, for all sludge types) with pre-treatment and increased with total solids concentration. The pre-treated sludge, namely, sterilized and hydrolyzed sludge showed higher microbial growth (1-2 log cycles increase in comparison to raw sludge) suggesting their susceptibility to microbial degradation. The C:N ratio decreased with pretreatment (raw sludge > sterilized > hydrolyzed) during biodegradation. Although the metal concentration increased in incubated hydrolyzed sludge, the final concentration was within the regulatory norms for agriculture application. Thus, pretreatment of sludge resulted in increase in biodegradability making it an excellent proponent for fermented value-added products.