Enhancing cellulose acetate biodegradability in cigarette filters: an in-depth analysis of thermal alkaline pretreatment, microbial dynamics, and breakdown pathway prediction.

BACKGROUND: The demand for bioplastics has increased exponentially as they have emerged as alternatives to petrochemical plastics. However, there is a substantial lack of knowledge regarding bioplastic degradation. This study developed a novel pretreatment method to improve the accessibility of a bioplastic substrate for biodegradation. In this study, cellulose acetate, a bioplastic found in the world's most littered waste, e.g. cigarette filters, was selected as a potential substrate. Before anaerobic digestion, three thermal alkaline pretreatments: TA 30 °C, TA 90 °C, and TA 121 °C, were used to evaluate their effects on the chemical alterations of cellulose acetate. RESULT: The ester groups in cellulose acetate were significantly reduced by the TA 30 °C pretreatment, as seen by a decrease in C = O stretching vibrations and shortening of C - O stretches (1,270 ∼ 1,210 cm- 1), indicating effective removal of acetyl groups. This pretreatment significantly enhanced cellulose acetate biodegradability to a maximum of 91%, surpassing the previously reported cellulose acetate degradation. Methane production increased to 695.0 ± 4 mL/g of volatile solid after TA 30 °C pretreatment, indicating enhanced cellulose acetate accessibility to microorganisms, which resulted in superior biogas production compared to the control (306.0 ± 10 mL/g of volatile solid). Diverse microbes in the anaerobic digestion system included hydrolytic (AB240379_g, Acetomicrobium, FN436103_g, etc.), fermentative, and volatile fatty acids degrading bacteria (JF417922_g, AB274492_g, Coprothermobacter, etc.), with Methanobacterium and Methanothermobacter being the sole hydrogenotrophic methanogens in the anaerobic digestion system. Additionally, an attempt to predict the pathway for the effective degradation of cellulose acetate from the microbial community in different pretreatment conditions. CONCLUSIONS: To the best of our knowledge, this is the first study to estimate the maximum cellulose acetate degradation rate, with a simple and cost-effective pretreatment procedure. This approach holds promise for mitigating the environmental impact of cellulose acetate of cigarette filters and presents a sustainable and economically viable waste management strategy.

Thermo-alkaline pretreatment of excess sludge: Effects of temperature on volatile fatty acids accumulation and microbial community.

In order to explore the role of thermal-alkaline pretreatment temperatures (TAPT) in sludge fermentation and the microbial characteristics, five groups (100, 120, 140, 160 °C and control group) were set up and the results showed that the increasing TAPT promoted the dissolution of soluble chemical oxygen demand (SCOD) and VFAs, but had slight influence on the release of NH4+-N and PO43--P. What's more, when it was 120 °C, the SCOD dissolution was comparable to that at 160 °C. Overall, 120 °C was the optimal condition, corresponding to the fact that the maximum release of SCOD was 8788.74 mg/L (2.63 times of the control group), the maximum dissolution of VFAs was 4596 mg/L (about 1.28 times of the control group). The trend of C/N was not significant. High-throughput sequencing showed that Firmicutes and Actinobacteriota were enriched with the temperature increasing, while Proteobacteria and Chloroflexi did not change significantly. Firmicutes was in a stable dominant position. Temperature conditions brought about significant changes in microbial interspecific interaction. Carbohydrate and amino acids had the highest metabolic abundance, especially at 120 °C group. The change rule of amino acid metabolism was similar to that of lipid metabolism, and the abundance of energy metabolism gradually increased with temperature. The protein metabolism was greatly affected by temperature. This study revealed the effect of microbial mechanism of TAPT on the sludge acid production efficiency.

Investigation of thermal alkaline pretreatment of primary and waste activated sludge on the energy efficiency of sludge digestion.

Because of the naturally limited anaerobic degradability and limited biogas yield of raw sludge (RS), this study aims to increase the biogas production of primary sludge (PS) and waste activated sludge (WAS) by the integration of thermal alkaline process (TAP). PH 11 is confirmed to be the most suitable pH value for the TAP of both sludges. Moreover, with the pretreatment at pH 11 and 160 °C (6 bar) for 30 min, the investigated PSs and WASs achieved an increased biogas production of up to 81 % and 72 %, respectively. The improved net electricity production of WASs after TAP varied between 15-43 % compared to conventional WAS digestion. However, the TAP of PS at pH 11 enhanced the biogas production by 1-81 %, which did not constantly contribute to an improved net electricity production.

Elucidating the production and inhibition of melanoidins products on anaerobic digestion after thermal-alkaline pretreatment.

The refractory organics released from waste activated sludge (WAS) are unwanted produced in thermal-alkaline pretreatment, which are not well documented. In this study, we refer to them as melanoidins products (MPs) with characteristics of high molecular weight and inhibition to microbes. The results showed that these MPs from thermal-alkaline (80 °C and pH 10) pretreatment of WAS were identified with a broad molecular weight (>1000 Da). Dark-colored MPs were further verified from glucose and tryptophan as the model components, with values of UV280 and UV420 increasing. The produced MPs with a molecular weight of 1220, 6835, and even 21,200,000 Da were confirmed by SEC-HPLC. Unexpectedly, MPs were found to be electroactive with higher redox peak values than that of humic acids, which were almost not degraded by anaerobes as revealed by SEC-HPLC and 3D-EEM spectra. For the first time, the results demonstrated that MPs delayed volatile fatty acids production and reduced the methane yield (22-26% lower), which was likely attributed to the toxicity and/or electrons competition with anaerobes such as Methanosaeta. Thus, it is clear that MPs negatively impact anaerobic digestion after thermal-alkaline pretreatment, which shall be re-evaluated to minimize MPs when producing biochemicals from WAS.

The capture technology matters: Composition of municipal wastewater solids drives complexity of microbial community structure and volatile fatty acid profile during anaerobic fermentation.

The production of volatile fatty acids (VFAs) represents a relevant option to valorize municipal wastewater (MWW). In this context, different capture technologies can be used to recover organic carbon from wastewater in form of solids, while pre-treatment of those solids has the potential to increase VFA production during subsequent fermentation. Our study investigates how VFA composition produced by fermentation is influenced (i) by the choice of the capture technology, as well as (ii) by the use of thermal alkaline pre-treatment (TAP). Therefore, the fermentation of solids originating from a primary settler, a micro-sieve, and a high-rate activated sludge (HRAS) system was investigated in continuous lab-scale fermenters, with and without TAP. Our study demonstrates that the capture technology strongly influences the composition of the produced solids, which in turn drives the complexity of the fermenter's microbial community and ultimately, of the VFA composition. Solids captured with the primary settler or micro-sieve consisted primarily of polysaccharides, and led to the establishment of a microbial community specialized in the degradation of complex carbohydrates. The produced VFA composition was relatively simple, with acetate and propionate accounting for >90% of the VFAs. In contrast, the HRAS system produced biomass-rich solids associated with higher protein contents. The microbial community which then developed in the fermenter was therefore more diversified and capable of converting a wider range of substrates (polysaccharides, proteins, amino acids). Ultimately, the produced VFA composition was more complex, with equal fractions of isoacids and propionate (both ~20%), while acetate remained the dominant acid (~50%). Finally, TAP did not significantly modify the VFA composition while increasing VFA yields on HRAS and sieved material by 35% and 20%, respectively. Overall, we demonstrated that the selection of the technology used to capture organic substrates from MWW governs the composition of the VFA cocktail, ultimately with implications for their further utilization.

Effects of low- and high-temperature thermal-alkaline pretreatments on anaerobic digestion of waste activated sludge.

To compare the effects of low- and high-temperature thermal-alkaline pretreatments (LTTAP, 60 ± 1 °C, pH 12.0 ± 0.1, 30 min and HTTAP, 160 ± 1 °C, pH 12.0 ± 0.1, 30 min, respectively) on anaerobic digestion (AD) of waste activated sludge, long-term and semi-continuous experiments were conducted in three laboratory continuous stirred tank reactors. The experimental results showed that the two pretreatments increased the methane yield of sludge from 89.20 ± 2.41 mL/g added volatile solids (VS) to 117.50 ± 5.27 mL/g added VS (LTTAP) and 156.40 ± 2.99 mL/g added VS (HTTAP). After AD, the reduction of sludge (volatile solid) increased from 32.91 ± 0.27% to 44.17 ± 1.53% (LTTAP), and 50.86 ± 1.18% (HTTAP), and the abundance of pathogenic bacteria decreased from 6.53% to 0.38% (LTTAP) and 0.14% (HTTAP). LTTAP enhanced both hydrogentrophic and acetoclastic methanogenis and HTTAP only enhanced acetoclastic methanogenis. Additionally, the energy efficiency of HTTAP and its subsequent AD was lower than that of LTTAP and its subsequent AD.

Comparison of two advanced anaerobic digestions of sewage sludge with high-temperature thermal pretreatment and low-temperature thermal-alkaline pretreatment.

Semi-continuous experiments were conducted to compare the performances and energy efficiencies of two advanced anaerobic digestions (AAD) of sewage sludge with high-temperature thermal pretreatment (HTTP, 160 ± 1 °C and 0.55 MPa for 30 min) and low-temperature thermal-alkaline pretreatment (LTTAP, 60 ± 1 °C and pH 12.0 ± 0.1 for 30 min), which had similar sludge disintegration degree (9.44-9.48%). At the steady period of a SRT 20 d, the two AAD had similar methane production (150.22 ± 9.55 ml/L/d and 151.02 ± 12.56 ml/L/d) and organic matter removals (22.54 ± 2.84% and 23.15 ± 2.46% for volatile solids-VS). The results of high-throughput sequencing showed that the methanogenic pathways of the two AAD were strictly hydrogenotrophic (AAD with HTTP) and hydrogenotrophic/acetoclastic methanogenesis (AAD with LTTAP), respectively. The energy balance analysis suggested that the AAD with LTTAP was superior to that with HTTP because the former had a higher energy efficiency (1.610) than the latter (1.358).

Pilot study of thermal alkaline pretreatment of waste activated sludge: Seasonal effects on anaerobic digestion and impact on dewaterability and refractory COD.

Thermal alkaline pretreatment (TAP) of waste activate sludge (WAS) was carried out in pilot-scale over a year to investigate its seasonal effects on anaerobic digestion and its impact on dewaterability, sludge liquor quality and formation of soluble refractory COD (sCODref). Temperature of TAP was set at 65-70 °C and pH was increased by initial dosing of sodium hydroxide [NaOH] (50% w/w, 1-2.5 mL/L sludge) as alkali agent following 2-2.5 h reaction time. Pilot digesters were fed with primary sludge (PS) and hydrolyzed WAS (HWAS) and compared to a reference digester fed with PS and untreated WAS. Biogas yield increase due to TAP of WAS showed a sinusoidal trend throughout the year with maximum in summer (+42%), minimum in winter (+3%) and average of +20%, indicating a strong seasonal effect on TAP efficiency. Ammonium [NH4+-N], orthophosphate [PO43--P] and sulphate [SO42-] in sludge liquor increased by 34.6%, 17.0% and 21.6% with TAP, respectively. Centrifugation tests showed no significant difference in dewaterability of both digestates with respect to total solids of sludge cake. Normalized capillary suction time of digestate increased due to TAP, indicating a lower capability for water release. Furthermore, detected sCODref after batch aerobic biodegradation tests showed an increase of 30.3% with TAP. Hence, implementation of TAP of WAS in full-scale will potentially lead to an increase of 0.8-1.1 mg/L of sCODref in effluent of six wastewater treatment plants (WWTP) in Berlin. In conclusion, TAP of WAS leads to increase in biogas production with a slighter negative impact on effluent COD quality than high-temperature thermal hydrolysis.

Effects of sludge thermal-alkaline pretreatment on cationic red X-GRL adsorption onto pyrolysis biochar of sewage sludge.

Thermal-alkaline pretreatment has traditionally been used to enhance anaerobic sludge digestion. In this study, after removing the supernatant, which could be used in anaerobic digestion, the Residual Solids of Thermal-Alkaline pretreated sewage Sludge (RSTAS) were used to prepare biochar via pyrolysis, which could then adsorb Cationic Red X-GRL(X-GRL). The experimental results showed that the RSTAS-biochar had a higher BET surface area and total pore volume than the biochar prepared from raw sludge (RS) (43.5% and 33.3%, respectively). The pretreatment enhanced the X-GRL adsorption capacity of the biochar by 1.5-49.2% at dosages between 12.5-100.0g/g, and the highest adsorption capacity increased from 39.1mg/g to 47.6mg/g. The biochar from RSTAS had a wider application pH range for X-GRL adsorption. The kinetics and isotherms for X-GRL adsorption onto the two biochars were well fitted to the pseudo-second-order and Langmuir isotherm models, respectively, which suggested that thermal-alkaline pretreatment had little effect on the adsorption mechanisms of X-GRL onto biochar.

Chicken feather valorization by thermal alkaline pretreatment followed by enzymatic hydrolysis for protein-rich hydrolysate production.

A huge amount of feathers is generated as a waste every year. Feathers can be a protein source if it is treated with an appropriate method. The present study investigates feasibility of autoclave alkaline and microwave alkaline pretreatments to be combined with enzymatic treatment for feather solubilization and protein production. Hydrolysis of chicken feather by autoclave alkaline pretreatment followed by an enzymatic method (AAS) or microwave alkaline pretreatment followed by an enzymatic method (MAS) was optimized by response surface methodology. Various NaOH concentrations for autoclave alkaline pretreatment (0.01-0.1 M) and microwave-alkaline pretreatment (0.01-0.05 M) were applied. The holding time for both pretreatments ranged from 1 to 10 min. The pretreated feathers were subjected to enzymatic hydrolysis using a commercial enzyme prior to analysis of protein content, feather solubilization, functional groups, and elemental composition (carbon, hydrogen, nitrogen and sulfur) of the treated feathers. The results revealed that both autoclave alkaline pretreatment and microwave alkaline pretreatment under optimized conditions of 0.068 M NaOH, 2 min holding time, 105 °C and 450 W, 0.05 M NaOH for 10 min, respectively, enhanced the subsequent Savinase hydrolysis of chicken feathers to achieve more than 80% degradation and more than 70% protein recovery. Fourier transform infrared spectroscopy results showed that both thermal-alkaline pretreatments weakened the structure of the feather. Reduction of carbon, nitrogen, and sulfur occurred in both thermal-alkaline pretreatments of feathers indicating degradation of the feather as well as protein release. Thermal-alkaline pretreatment may be a promising method for enhancing the enzymatic hydrolysis of chicken feathers and for producing a protein-rich hydrolysate.

Pre-separation of ammonium content during high solid thermal-alkaline pretreatment to mitigate ammonia inhibition: Kinetics and feasibility analysis.

The feasibility of ammonia pre-separation during the thermal-alkaline pretreatment (TAP) of waste activated sludge was evaluated to mitigate ammonia inhibition during high solid anaerobic digestion (HSAD). The results showed that the TAP increased the organics hydrolysis rate as much as 77% compared to the thermal hydrolysis pretreatment (THP). The production and separation of the ammonia during the TAP exhibited a linear relationship with the hydrolysis of organics and the Emerson model. The pre-separation ratio of the free ammonia nitrogen exceeded 98.00% at a lime dosage exceeding 0.021 g CaO/g TS. However, the separation ratio of the total ammonia nitrogen (TAN) was hindered by its production ratio. Compared to the THP, the TAP increased the methane production rate under similar production yield. A mass flow analysis indicated that the TAP-HSAD process reduced the volume of the digester compared to the THP-HSAD process and the recirculated HSAD-TAP process recovered 45% of the nitrogen in the waste activated sludge.

Improving methane production from digested manure biofibers by mechanical and thermal alkaline pretreatment.

Animal manure digestion is associated with limited methane production, due to the high content in fibers, which are hardly degradable lignocellulosic compounds. In this study, different mechanical and thermal alkaline pretreatment methods were applied to partially degradable fibers, separated from the effluent stream of biogas reactors. Batch and continuous experiments were conducted to evaluate the efficiency of these pretreatments. In batch experiments, the mechanical pretreatment improved the degradability up to 45%. Even higher efficiency was shown by applying thermal alkaline pretreatments, enhancing fibers degradability by more than 4-fold. In continuous experiments, the thermal alkaline pretreatment, using 6% NaOH at 55°C was proven to be the most efficient pretreatment method as the methane production was increased by 26%. The findings demonstrated that the methane production of the biogas plants can be increased by further exploiting the fraction of the digested manure fibers which are discarded in the post-storage tank.

Anaerobic digestion of recalcitrant textile dyeing sludge with alternative pretreatment strategies.

Abundant organic compounds in textile dyeing sludge (TDS) provide possibility for its anaerobic digestion (AD) treatment. However, preliminary test showed little biogas generation in direct AD of the TDS during 20days. In order to improve the AD availability of TDS, alkaline, acid, thermal and thermal alkaline pretreatments were performed. Color and aromatic amines were specifically measured as extra characteristics for the AD of TDS. The rate-limiting steps of AD of TDS were slow hydrolysis rate and inhibited acidogenesis, which were somewhat overcome by pretreatments. Thermal alkaline pretreated TDS performed best enhancement on solubilisation. The biochemical methane potential tests revealed that thermal pretreated TDS showed highest total methane production of 55.9mL/gVSfed compared to the control with little methane generation. However, thermal alkaline pretreated TDS did not perform well in BMP test as expected. Moreover, the hydrophilicity of reactive dyes in TDS could seriously affect dewaterability of TDS.

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.