Enhancement mechanisms of short-time aerobic digestion for waste activated sludge in the presence of cocoamidopropyl betaine

Controlled Release of Amphoteric Surfactant from Mesoporous Nanosilica To Enhance Natural Gas Production at High Temperatures

Surfactants are widely used as foaming agents to remove liquid accumulation in gas wells, enhancing natural gas production. The surfactant used in traditional foam sticks was dissolved and released as foam in a short period, especially at elevated downhole temperatures. This often requires the addition of foam sticks to maintain foam. To solve this problem, this study studies the utilization of nano silica to incorporate the amphoteric surfactant, cocamidopropyl betaine (CAB), into the mesoporous structure of silica nanocomposite as foam sticks for controlled release of CAB. Mesoporous nano silica was prepared by a sol-gel acid-catalyzed process with a silica precursor. The formation of nanocomposite solid sticks containing the amphoteric surfactant was achieved by aging and drying. The composite was characterized by various techniques: infrared spectroscopy, thermogravimetric analysis, energy-dispersive spectrometry, scanning electron microscopy, transmission electron microscopy, and small-angle X-ray diffraction. Results showed that 49.3% of CAB was encapsulated within the mesoporous structure of 30-50 nm nano silica. CAB release over time in aqueous solution at 130 °C exhibited 10.1% surfactant left in the nanocomposite after 72 h, as determined by thermal analysis. Surfactant release was systematically evaluated through foam performance tests. The study revealed that CAB could be control-released over 168 h via CAB diffusion from mesoporous silica. This study provides a longer-lasting foam method to enhance gas production by utilizing mesoporous silica as a control release medium for gas well deliquification.

Phycoremediation potential and agar yield of red macroalgae (Gracilaria corticata) against HEDP (hydroxyethylidene diphosphonic acid) and CAPB (cocoamidopropyl betaine) detergents and the heavy metal pollutants

The discharge of raw industrial, agricultural, and domestic wastes leads to an increase in heavy metal (HM) burden and detergents in aquatic environs, which can have destructive effects on aquatic organisms. Agarophyte Gracilaria corticata, a major component of seaweed flora of the southern coast of Iran (Bushehr) that contains agar and red pigments, is one of the economically valuable red marine algae. Agar is one of the important polysaccharides with high economic value, widely used in pharmaceutical, medicinal, and cosmetic product manufacturing industries. The aim of this work was to investigate the effect of 5 HMs and two common surfactants in household and industrial detergents on the agar yield, appearance color, and the red algae's phycoremediation potential against HMs. The metal ions were Zn(II), Cu(II), Ni(II), Mn(II), and Cr(VI), and the surfactants were HEDP and CAPB. The analysis results of samples cultured for 60 days in seawater and polluted environments showed that G. corticata can accumulate copper and nickel. In the presence of detergents without HMs, the amount of extracted agar significantly increased compared to the control sample with no change in algae color. But with increasing concentration of HMs, the amount of agar in seaweed samples decreased significantly, and the algae discolored from red to dark green or yellowish-green color (signs of death in the algae). These results show that increasing of HM pollution and detergents can lead to toxicological effects and reduce the species diversity of red seaweeds in the future.

Response of antibiotic resistance genes and microbial niches to dissolved oxygen in an oxygen-based membrane biofilm reactor during greywater treatment

Linear alkylbenzene sulfonates (LAS) in greywater (GW) will simulate antibiotic resistance genes (ARGs) production in the biofilm-based system. Our study emphasizes the dissolved oxygen (DO)-dependent ARGs accumulation and microbial niches succession in an oxygen-based membrane biofilm reactor (O₂-MBfR) treating GW, as well as revealing the key roles of EPS. Changing DO concentrations led to significant differences in ARGs production, EPS secretion and microbial communities, as well as the organics and nitrogen removal efficiency. Increasing DO concentration from 0.2 to 0.4 mg/L led to improved organics (> 90%) and nitrogen removal, as well as less EPS (especially for proteins and carbohydrates) and ARGs accumulation (e.g., intI-1, korB and sul-2) in the biofilm; the high-DO-concentration accumulated microbial niches, including Flavobacteriaceae and Cyanobacteria that revealed by LEfSe analysis, contributed to both nitrogen reduction and organics biodegradation. While, the inefficient electron acceptor at low DO conditions (0.2 mg/L) reduced the organics and nitrogen removal efficiency, as well as the improved accumulation of EPS in biofilm; high EPS enabled the capture of residual LAS from the liquid phase, which stimulated the production of ARGs by the distinct microbial community compositions. These findings suggested the DO-based ARGs reduction regulation strategy in the O₂-MBfR treating GW.

Assessment and optimization of the oxygen based membrane biofilm reactor as a novel technology for source-diverted greywater treatment

The oxygen based membrane biofilm (O₂-MBfR) has been proved to be a novel technology in treating greywater (GW) and response surface methodology (RSM) was used to model the removal of chemical oxygen demand (COD) and total nitrogen (TN) with operation parameters COD/TN ratio, system pH and lumen air pressure (LAP). Results indicated that the all target single factors affect GW treatment efficiency, and the regression model with central composite design (CCD) showed good agreement with the experimental results with high R² and R2 adj values (all >0.97) for all the target responses. Statistical evaluation revealed that system pH was the most significant parameter affecting COD and TN removal, followed by COD/TN ratio and LAP. The interaction between COD/TN ratio and system pH also played an important role on the GW treatment. The optimized maximum removal of COD (96.48%) and TN (133 g N/m²-day) were achieved with the COD/TN ratio 17.76 g COD/g TN, system pH 7.10 and LAP 1.00 psi. Thus, RSM combined with CCD could be used for predicting the organics and nitrogen removal during GW treatment in the O₂-MBfR.

Calcium peroxide significantly enhances volatile solids destruction in aerobic sludge digestion through improving sludge biodegradability

This work put up a novel strategy of applying calcium peroxide (CaO₂) in aerobic sludge digestion and provided insights into such system. The degradation percentage of sludge and total inorganic nitrogen production in the digesters with CaO₂ at 0.02 g/g-VS-WAS increased by 25.8% and 18.8% of control. CaO₂ addition allowed various key microbes related to organics degradation to accumulate in the system. Moreover, the modelling and chemical (i.e., excitation emission matrix (EEM) fluorescence and fourier transformation spectroscopy (FTIR)) analyses revealed that CaO₂ addition enhanced sludge biodegradability with more release of biodegradable organics and increased degradation of recalcitrant organics, which can be transformed into biodegradable organics with the action of CaO₂. Subsequent transformation test indicated that CaO₂ enabled to promote hydrolysis and catabolism of biodegradable substrates in sludge. Further investigations on function mechanism suggested that CaO₂ carried on positive action for sludge aerobic digestion mainly through the enhancement by ·OH.

Removal kinetics of linear alkylbenzene sulfonate in a batch-operated oxygen based membrane biofilm reactor treating greywater: Quantitative differentiation of adsorption and biodegradation

Oxygen-based membrane biofilm reactor (O₂-MBfR) is a unique technique for high linear alkylbenzene sulfonate (LAS)-containing greywater (GW) treatment. Despite the efficient removal of LAS, the dynamics of how it is taken up and the quantitative differentiation of adsorption and biodegradation are largely undefined. In this study, we tracked the fate of LAS, chemical oxygen demand and nitrogen in various systems: GW, GW with inactivated sludge (InAS) and GW with activated sludge (AS). We determined the distribution of biodegraded-, free-, and extracellular polymeric substances (EPS)-attached LAS, and we also developed a model to simulate all the steps. Results showed that AS exhibited high live cells proportion and microbial activity, but the opposite trend for GW and InAS. Both of nitrogen and organics could be simultaneously and efficiently removed in the AS inoculated system. The two-step model for LAS uptake and biodegradation represented the experimental results well. EPS adsorption led to the fast LAS accumulation in biofilm, and biodegradation led to the continuous removal of LAS in the system. After operated for 24 h, biodegradation and EPS accumulation of LAS were 94% and 4%, respectively, and the residual soluble LAS was lower than 1%. This work lays the foundation for using O₂-MBfR to treat GW and other types of wastewater, and understanding the key roles of EPS and the mathematical model of LAS removal in the system.

The influent COD/N ratio controlled the linear alkylbenzene sulfonate biodegradation and extracellular polymeric substances accumulation in an oxygen-based membrane biofilm reactor

This work evaluated the fates of linear alkylbenzene sulfonate (LAS), chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), and total nitrogen (TN) when treating greywater (GW) in an oxygen-based membrane biofilm reactor (O₂-MBfR). An influent ratio of chemical oxygen demand to total nitrogen (COD/TN) of 20 g COD/g N gave the best removals of LAS, COD, NH₄⁺-N and TN, and it also had the greatest EPS accumulation in the biofilm. Higher EPS and improved performance were linked to increases in the relative abundances of bacteria able to biodegrade LAS (Zoogloea, Pseudomonas, Parvibaculum, Magnetospirillum and Mycobacterium) and to nitrify (Nitrosomonas and Nitrospira), as well as to ammonia oxidation related enzyme (ammonia monooxygenase). The EPS was dominated by protein, which played a key role in adsorbing LAS, achieving short-time protection from LAS toxicity and allowed LAS biodegradation. Continuous high-efficiency removal of LAS alleviated LAS toxicity to microbial physiological functions, including nitrification, nitrate respiration, the tricarboxylic acid (TCA) cycle, and adenosine triphosphate (ATP) production, achieving the stable high-efficient simultaneous removal of organics and nitrogen in the O₂-MBfR.

Key role of soluble microbial products in waste activated sludge reduction by synergetic combination of cocoamidopropyl betaine and alkalinity in the short-time aerobic digestion system

As a widely used ampholytic surfactant, cocoamidopropyl betaine (CAPB) has been improved to enhance waste activated sludge (WAS) reduction in the short-time aerobic digestion (STAD) system, but how system pH value affects the synergetic combined process has not been discussed. This research evaluated how alkalinity affects soluble microbial products (SMP) dynamics and WAS reduction in the synergetic system. After adding CAPB, the biodegradation rate constant of VSS (k_VSS), TCOD (k_TCOD) and CAPB (k_CAPB) were much higher than that of without adding CAPB; pH value at 7.0-8.0 showed the maximum specific oxygen uptake rate (SOUR) of WAS, leading to the highest WAS reduction efficiency. Further study indicated that CAPB can significantly improve the release of extracellular polymeric substances (EPS), leading to the increased SMP concentrations and low molecular weight fractions (MWF) proportions in SMP; more SMP with low MWF fraction led to the increased SOUR, thus further accelerate the WAS reduction; increasing pH could improve the foaminess and solubility of CAPB, thus further improve the organics release and SMP accumulation, which could be quickly removed in the system. This findings lay the foundation of the practical application of the synergetic combination system in WAS reduction.

Three-dimension oxygen gradient induced low energy input for grey water treatment in an oxygen-based membrane biofilm reactor

Grey water (GW) containing high levels of linear alkylbenzene sulfonates (LAS) can be a threat to human health and organisms in the environment if not treated properly. Although aerobic treatment could achieve high organics removal efficiency, conventional aeration can lead to serious foaming and energy waste. Here, we systematically evaluated an oxygen based membrane biofilm reactor (O₂-MBfR) for its capacity to simultaneously remove organics and nitrogen from GW. The dissolved oxygen (DO) concentration inside the reactor was maintained at 0.4 mg/L by gradually controlling the lumen air pressure. Results showed that the O₂-MBfR achieved high removal efficiency of total chemical oxygen demand (TCOD), total linear alkylbenzene sulfonates (LAS) and total nitrogen (TN) of 89.7%, 99.1% and 78.1%, respectively, with a hydraulic retention time (HRT) of 7.5 h. Lower HRT (7.0 h) led to the accumulation of LAS in the biofilm, which caused cell lysis and damaged the O₂-MBfR system, leading to a discernible and continuous decline of the reactor performance. The O₂-MBfR design completely eliminated foaming formation and the three-dimension oxygen gradient design led to low air pressure inside the membrane fiber, which enabled the high removal efficiency for both organics and nitrogen with low energy input and GW treatment cost, providing the fundamental knowledge for practical application of O₂-MBfR in wastewater treatment.

Treatment of grey water (GW) with high linear alkylbenzene sulfonates (LAS) content and carbon/nitrogen (C/N) ratio in an oxygen-based membrane biofilm reactor (O2-MBfR)

Grey water (GW) containing high levels of linear alkylbenzene sulfonates (LAS) can be a threat to the human health and organisms in the environment if not treated properly. Although aerobic treatment may achieve high GW treatment efficacy, conventional aeration can lead to serious foaming. Here, we firstly and systematically evaluated an oxygen-based membrane biofilm reactor (O₂-MBfR) for its capacity to simultaneous remove organics and nitrogen from greywater with high LAS levels and carbon/nitrogen (C/N) ratios. After a five-day startup period, multifarious microorganisms formed multifunctional biofilms and the MBfR achieved high removal rates of chemical oxygen demand (COD), LAS, and total nitrogen (TN) of 88.4%, 95.6%, and 80%, respectively, with a hydraulic retention time of 7.86 h. Higher organics loading (5.53 g TCOD/m²-day) caused cell lysis and damaged the O₂-MBfR system, leading to a discernible and continuous decline of the reactor performance. The O₂-MBfR design completely eliminated foaming formation. LAS -biodegrading-rich genus containing Clostridium, Parvibaculum, Dechloromonas, Desulfovibrio, Mycobacterium, Pseudomonas, and Zoogloea enable the nearly complete removal of LAS even under high C/N conditions. Results demonstrated that the O₂-MBfR technology is feasible for treating GW containing high LAS and C/N ratio, while remaining free of foaming formation, and at a low cost due to high O₂ utilization rates.

DNA-based stable isotope probing identifies triclosan degraders in nitrification systems under different surfactants

Three widely-used surfactants, rhamnolipid (RL), sophorolipid (SL) and sodium dodecyl benzene sulfonate (SDBS), were chosen to investigate their effects on the nitrification systems treating step-wised triclosan (TCS). Surfactants had little effects on nitrification. Surfactants could promote the desorption of TCS and enhance the TCS biodegradation in nitrification systems. And TCS biodegradation efficiencies obtained with RL, SL and SDBS were 1.25, 1.23 and 1.14 times higher than the control with 9.0 mg/L TCS, respectively. Illumina MiSeq sequencing showed that Amaricoccus could be resistant to TCS. And Amaricoccus, detected with RL, SL and SDBS, were more abundant than the control. DNA-based stable isotope probing assays revealed Amaricoccus was the major TCS degrader. And the addition of surfactants could obviously increase the diversity of active TCS degraders, especially for biosurfactants. It seems that the addition of surfactants showed positive effects for the nitrification systems treating TCS wastewater.

Promoting waste activated sludge reduction by linear alkylbenzene sulfonates: Surfactant dose control extracellular polymeric substances solubilization and microbial community succession

Short-time aerobic digestion (STAD) was proved to promote the reduction of waste activated sludge (WAS). This study systematically disclosed the influential characteristics and mechanisms of linear alkylbenzene sulfonates (LAS) dosage on the reduction of WAS in STAD system. Flow cytometer (FC) combined with SYTOX Green (SG) dye was used to differentiate extracellular polymeric substances (EPS) release and cell lysis of WAS during STAD process. LAS lower than 0.10 g/g total suspended solids (TSS) brought about EPS solubilization and the decrease of sludge floc size, and the accumulated soluble microbial products (SMP) could be biodegraded by heterotrophs. Moreover, the activity of microorganisms (denoted as specific oxygen uptake rate (SOUR)) and proportion of bacteria functional for LAS and SMP biodegradation dramatically increased, leading to a high LAS biodegradation rate (k_LAS) and increased WAS biodegradation rate (k_{COD, WAS}). Even more LAS (> 0.10 g/g TSS) caused cell lysis, leading to the decreased k_TCOD and k_LAS, and therefore inhibit the reduction of WAS. High WAS reduction and LAS biodegradation rate were achieved at the LAS dosage of 0.10 g/g TSS in STAD system. This study lays the foundation for improving WAS reduction by optimizing surfactant dose in STAD system.

pH dependent of the waste activated sludge reduction by short-time aerobic digestion (STAD) process

The short-time aerobic digestion (STAD) process has been found to be a unique and significant technique for the stabilization of waste activated sludge (WAS), but the influences of the system pH on the STAD process was unclear. This study systematically disclosed the influences of the system pH on the STAD process of WAS. Under neutral or weak alkaline conditions, although the biodegradation rates of VSS (~0.0085 h^-1) were low, high biodegradation rates of TCOD (k_TCOD) (~0.0096 h^-1) were achieved. Less releases of the biopolymers from the WAS led to low concentrations of STOC, UV₂₅₄, the low MW organic matters, NH₄⁺ - N and PO₄^3- - P in the supernatant. However, the appropriate pH for the microorganisms improved SOUR, indicating that the released substances were further reused or biodegraded by the microorganisms. Under acidic or alkaline conditions, the biodegradation rates of VSS (0.009-0.019 h^-1) and TCOD (k_TCOD) (0.005-0.009 h^-1) were opposite with those under neutral or weak alkaline conditions. The releases of the biopolymers were increased, leading to high concentrations of STOC, UV₂₅₄, the low MW organic matters, PO₄^3- - P and NH₄⁺ - N in the supernatant. However, the extreme pH inhibited the microbial activity. The SOURs were only 0.0097 h^-1 and 0.0053 h^-1 for system pH of 8.0 and 4.0, respectively. Accordingly, neutral and weak alkaline conditions should be more suitable for the STAD process of WAS. This work lays the foundation for optimizing system pH for the reduction of WAS in STAD system.

Nitrogen aeration alters the spatial distribution and metal adsorption of extracellular polymeric substances in waste-activated sludge

Extracellular polymeric substances (EPS) extracted from waste-activated sludge (WAS) have the potential to remove heavy metal ions from wastewater; both the spatial distribution and metal adsorption of EPS from WAS after nitrogen aeration were systematically investigated in this study. Compared with air aeration, nitrogen aeration significantly improved the contents of proteins (PN) and polysaccharides (PS) in the Slime-EPS (S-EPS) and loosely-bound EPS (LB-EPS), significantly increased the PS content, and slightly increased the PN content in the tightly-bound EPS (TB-EPS). The variations in the fluorescence intensities (FI) of the peaks I and II for the S-EPS, LB-EPS and TB-EPS were basically consistent with the abovementioned variations in the concentrations of these EPS. Notably, nitrogen aeration dramatically improved the content of protein-like substances in the LB-EPS. For the same aeration time, the Pb²⁺ reclamation rates obtained by the LB-EPS extracted from the nitrogen-aerated WAS were much higher than those achieved by the LB-EPS extracted from the air-aerated WAS. The FTIR analyses further indicated that nitrogen aeration improved the contents of the functional groups, especially –OH, –COOH and –NH₂, responsible for binding heavy metals, in both the LB-EPS and TB-EPS. The SEM analyses verified that the nitrogen scours contributed to the EPS release, and Pb²⁺ reclamation was achieved via the attachment of Pb²⁺ onto the edge of the EPS. The influences of the nitrogen aeration on the spatial distribution and metal adsorption of the EPS in WAS were revealed for the first time in this study. Thus, this study lays the foundation for the application of nitrogen aeration in the resource utilization of WAS.

Nitrogen aeration was superior to air aeration because of the higher EPS production and Pb²⁺ adsorption in the utilization of WAS.

Simultaneously enhanced biopolymers production and sludge dewaterability of waste activated sludge by synergetic integration process of short-time aerobic digestion with cocoamidopropyl betaine and calcium oxide

Waste activated sludge (WAS) has seriously threatened the environment safety and the public health due to its rapid growth and complex components. Simultaneously enhanced the biopolymers production and the sludge dewaterability of WAS were investigated by synergetic integration process of the short-time aerobic digestion (STAD) with cocoamidopropyl betaine (CAPB) and calcium oxide (CaO). STAD could improve the biopolymers production by biosynthesis. CAPB could further significantly enhance the biopolymers production and optimized the constituents. CaO (0.1-0.2 g/g TSS) could dramatically enhance the sludge dewaterability by forming a multi-grid skeleton in WAS, while the biopolymers production could almost remain stable. Especially, the synergetic integration process of STAD with 0.1 g CAPB/g TSS for 8 h and 0.1 g CaO/g TSS could cost-effectively enhance both the biopolymers production and the sludge dewaterability. The produced biopolymers showed strong adsorbability for heavy metals (eg, 375 mg Cu²⁺/g biopolymers). Accordingly, the developed novel process is of big significance for resource utilization and volume reduction of WAS.

Effect of Bioaugmentation on Biogas Yields and Kinetics in Anaerobic Digestion of Sewage Sludge

Bioaugmentation with a mixture of microorganisms (Bacteria and Archaea) was applied to improve the anaerobic digestion of sewage sludge. The study was performed in reactors operating at a temperature of 35 °C in semi-flow mode. Three runs with different doses of bioaugmenting mixture were conducted. Bioaugmentation of sewage sludge improved fermentation and allowed satisfactory biogas/methane yields and a biodegradation efficiency of more than 46%, despite the decrease in hydraulic retention time (HRT) from 20 d to 16.7 d. Moreover, in terms of biogas production, the rate constant k increased from 0.071 h⁻¹ to 0.087 h⁻¹ as doses of the bioaugmenting mixture were increased, as compared to values of 0.066 h⁻¹ and 0.069 h⁻¹ obtained with sewage sludge alone. Next-generation sequencing revealed that Cytophaga sp. predominated among Bacteria in digesters and that the hydrogenotrophic methanogen Methanoculleus sp. was the most abundant genus among Archaea.

The effect of phosphate buffer on improving the performance of autothermal thermophilic aerobic digestion for sewage sludge

The influence of phosphate buffer on the stabilization of sewage sludge was investigated in autothermal thermophilic aerobic digestion (ATAD). A concentration series of 0.005, 0.01, 0.02 and 0.03 mol phosphate buffer for each liter of sludge was adopted. The phosphate buffer significantly enhanced the performance of the ATAD for sewage sludge. The highest VS removal was achieved by the group with 0.01 mol L^-1 phosphate buffer, and the stabilization time of the sludge was shortened by 9 days compared with that of the control. The group with the optimal dosage obtained the deepest stabilization level of sludge, which was reflected by the distribution of the particle size, and achieved 6.08% VS removal higher than that of the control in the end. Lower concentrations of carbon, nitrogen and phosphate in the supernatant were also achieved by proper dosing compared with those of the control.

Influencing characteristics of short-time aerobic digestion on spatial distribution and adsorption capacity of extracellular polymeric substances in waste activated sludge

The spatial distribution and adsorption capacity of extracellular polymeric substances (EPS) were systematically investigated for waste activated sludge (WAS) treated by a short-time aerobic digestion (STAD) process.