Polydimethyldiallylammonium chloride inhibits dark fermentative hydrogen production from waste activated sludge

Polydimethyldiallylammonium chloride (PDDA) is an excellent flocculant for wastewater purification and sludge dewatering, but whether it poses a threat to hydrogen production from waste activated sludge is not known. In this study, the effect and underlying mechanism of PDDA on the dark fermentation of sludge was investigated. The results showed that PDDA reduced cumulative hydrogen production from 3.8±0.1 to 2.4±0.1 mL/g volatile suspended solids at 40 g/kg total suspended solids. PDDA impeded the dark fermentation process by inhibiting the activity of key enzymes, presenting a stronger inhibitory effect on the hydrogen production process than the hydrogen consumption process. Additionally, PDDA inhibited Firmicutes by enriching other microorganisms, thereby impeding hydrogen production via the acetate pathway. This study deepens the understanding of the potential effects of PDDA on sludge treatment and provides a theoretical basis for alleviating the negative effects of quaternary ammonium-based cationic flocculants.

Design and application of gel coagulation-spontaneous flotation integrated process in water treatment: "Clouds in water"

The gel coagulation-spontaneous flotation (GCSF) process designed in this paper mainly rely on dissolved gas in water rather than auxiliary gas equipment to achieve spontaneous flotation. Compared with the traditional coagulation-dissolved air flotation method, GCSF has more stable flotation efficiency and shorter operation cycle under conventional hydraulic conditions. In this study, the GCSF scheme was applied for surface water treatment, and its operating efficiency, mechanism of action, and environmental implications were explored systematically. The results illustrate that the dosage ratio of sodium alginate (SA) to aluminum sulfate (AS) should be controlled in the range of approximately 1.5:1-2.5:1, and SA should be added 15∼120 s before AS during the coagulation process. Under these conditions, the adsorption cross-linking between SA and Al3+ promoted the generation of gel flocs and effectively encapsulated the dissolved gasses, thereby achieving a stable spontaneous flotation process and 80%-95% removal of pollutants. The purification efficiency of GCSF was positively correlated with pH 4-9, which was attributed to the enhanced hydrophobicity of the chains of organic polymer groups. The residual SA and aluminum concentration in effluent were lower than 1 and 0.05 mg/L, respectively, which guarantee the ecological security of GCSF application. In addition, the results of density functional theory calculations revealed that -OH and -AlO6 in cross-linked flocs could adsorb dissolved oxygen synergistically, while -OH combined with oxygen had a stronger binding energy and stable adsorption.

Potential of biogenic and non-biogenic waste materials as flocculant for algal biomass harvesting: Mechanism, parameters, challenges and future prospects

In this review article, waste materials (biogenic/non-biogenic) are focused as the flocculants for harvesting of algal biomass. Chemical flocculants are widely utilized for the effective harvesting of algal biomass at a commercial scale while the high cost is a major drawback. The waste materials-based flocculants (WMBF) are started to utilize as one of the cost-effective performance for dual benefits of waste minimization and reuse for sustainable recovery of biomass. The novelty of the article is articulated with the objective that presents an insight of WMBF, classification of WMBF, preparation methods of WMBF, mechanisms of flocculation, factors affecting flocculation-mechanism, challenges and future recommendations that are required for harvesting of algae. The WMBF are shown similar flocculation mechanisms and flocculation efficiencies as chemical flocculants. Thus, the utilization of waste material for the flocculation process of algal cells minimizes the waste load into the environment and transforms the waste materials into valuable resources.

Insights into the role of chitosan in hydrogen production by dark fermentation of waste activated sludge

Chitosan is widely used as a dewatering flocculant, but whether it affects hydrogen production from sludge anaerobic fermentation is unclear. This study aimed to elucidate the role of chitosan in the dark fermentation of waste activated sludge for hydrogen production. The results showed that chitosan had a negative effect on hydrogen production from sludge. Chitosan at 30 g/kg total suspended solids reduced hydrogen accumulation by 56.70 ± 1.22 % from 3.94 ± 0.12 to 1.71 ± 0.10 mL/g volatile suspended solids. Chitosan hindered the solubilization of sludge by flocculation, which reduced the available substrate for anaerobic fermentation. In addition, chitosan interfered with the electron transport system by reducing cytochrome C and caused lipid peroxidation by inducing reactive oxygen species, thereby inhibiting the activity of enzymes involved in anaerobic fermentation. Hydrogen production was reduced because hydrogen-producing processes (i.e., hydrolysis, acidification, and acetification) were inhibited more strongly than hydrogen-consuming processes (i.e., methanogenesis, sulfate reduction, and homoacetogenesis). Furthermore, chitosan enriched the abundance of Spirochaetaceae sp. and Holophagaceae sp., which occupied the survival space of hydrogen-producing microorganisms. This study reveals the potential impact of chitosan on hydrogen production in dark fermentation of sludge and provide direct evidence that chitosan triggers oxidative stress in anaerobic fermentation.

Uncovering the effect of polyethyleneimine on methane production in anaerobic digestion of sewage sludge

The potential effect of polyethyleneimine as a flocculant on anaerobic digestion of sludge was investigated. Polyethyleneimine above 12 g/kg total suspended solids inhibited the entire anaerobic digestion process including solubilization, hydrolysis, acidification, and methanogenesis. The addition of 24 g/kg total suspended solids polyethyleneimine reduced methane production from 167 ± 5 L/kg volatile suspended solids in the control reactor (without polyethyleneimine) to 141 ± 5 L/kg volatile suspended solids. Polyethyleneimine bound to extracellular polymeric substances, thus enhancing sludge agglomeration and hindering the release of organics. Meanwhile, the reduction of cytochrome C impeded electron transport, consequently curbed direct interspecies electron transfer. The adsorption of carbon dioxide by amine groups also hampered methane conversion. This study elucidated the concept that polyethyleneimine reduces mass transfer in anaerobic digestion, providing new insights into the potential behavior of flocculants in sludge treatment.

Polydimethyldiallylammonium chloride induces oxidative stress in anaerobic digestion of waste activated sludge

The effects and key mechanisms of polydimethyldiallylammonium chloride on anaerobic digestion of waste activated sludge were investigated. Polydimethyldiallylammonium chloride at 38.1 g/kg total solids substantially reduced cumulative methane production from 138.2 ± 5.5 to 49.4 ± 5.0 L CH₄/kg volatile solids added, a reduction of 64.3 ± 0.2%. The quaternary ammonium groups on polydimethyldiallylammonium chloride agglomerated sludge flocs by neutralizing negatively charged amino groups in in extracellular polymeric substances, which hindered the release of organic matter. Quaternary ammonium groups induce oxidative stress by inducing the production of reactive oxygen species, thereby inhibiting the activity of anaerobic digestive enzymes. In addition, quaternary amine groups reduced the abundance of hydrolyzing bacteria, acidifying bacteria, and acetylotrophic methanogens. Oxidative stress could be an underappreciated mechanism that quaternary ammonium groups deteriorate anaerobic digestion, which could be transformative for understanding the potential risks of quaternary ammonium cationic flocculants in biological sludge treatment.

Unraveling the role of polyferric chloride in anaerobic digestion of waste activated sludge

This study explored the effect of polyferric chloride (PFC) as a flocculant on waste activated sludge anaerobic digestion. The results verified that PFC has an inhibitory effect on methane production during anaerobic digestion. PFC with a concentration of 40 g/kg total suspended solids reduced methane production from 195 ± 2.10 to 156 ± 1.50 L/kg volatile suspended solids, a decrease of 20.0 ± 0.09%. PFC released hydroxyl polymers and Fe(III). Hydroxy polymers aggregated sludge flocs and hindered the release of dissolved organic matter. Fe(III) induced dissimilar iron reduction processes to contend with methyl-CoM for electrons, thereby further reducing methane production. In addition, PFC enriched iron-reducing bacteria and reduced the abundance of methanogens, resulting in microbial communities that are not conducive to methane production. This article puts forward innovative insights on the role of PFC in biological sludge treatment, which is expected to guide the flocculant selection during wastewater treatment.

Sequential modelling for carbohydrate and bioethanol production from Chlorella saccharophila CCALA 258: a complementary experimental and theoretical approach for microalgal bioethanol production

Bioethanol production from microalgal biomass is an attractive concept, and theoretical methods by which bioenergy can be produced indicate saving in both time and efficiency. The aim of the present study was to investigate the efficiencies of carbohydrate and bioethanol production by Chlorella saccharophila CCALA 258 using experimental, semiempirical, and theoretical methods, such as response surface methods (RSMs) and an artificial neural network (ANN) through sequential modeling. In addition, the interactive response surface modeling for determining the optimum conditions for the variables was assessed. The results indicated that the maximum bioethanol concentration was 11.20 g/L using the RSM model and 11.17 g/L using the ANN model under optimum conditions of 6% (v/v %) substrate and 4% (v/v %) inoculum at 96-h fermentation, pH 6, and 40 °C. In addition, the value of the experimental data for carbohydrate concentration was 0.2510 g/g biomass at ANN with the maximums of 50% (v/v) wastewater concentration, 4% (m/m) hydrogen peroxide concentration, and 6000 U/mL enzyme activity. Finally, although the RSM model was more effective than the ANN model for predicting bioethanol concentration, the ANN model yielded more precise values than the RSM model for carbohydrate concentration.

Understanding the synergistic mechanism of PAM-FeCl3 for improved sludge dewaterability

Hybrid flocculant polyacrylamide-ferric chloride (PAM-FeCl₃) was developed to improve the dewaterability of sewage sludge and the dewatering performance, properties of treated sludge, composition and morphology distribution of extracellular polymeric substance (EPS) were investigated. The physicochemical properties of the PAM-FeCl₃ were characterized, and its effectiveness as a sludge conditioner was evaluated. The results indicated that PAM-FeCl₃ conditioning was able to promote sludge dewaterability. Simultaneously, PAM-FeCl₃ neutralized the negative charges on the surface of sludge particles and increased the sludge floc size. Besides, PAM-FeCl₃ also formed a rough and porous floc structure that reduced sludge compressibility. Meanwhile, the exciting emission matrix analysis suggested that PAM-FeCl₃ can effectively disintegrate of EPS fraction in sludge and decompose the aromatic protein-like substances as well as the humic acid-like substances in EPS. Additionally, the larger sludge floc formation, electrostatic interaction and adsorption bridging effect resulted in compression of sludge structure and the decomposition of EPS fractions and improved sludge dewatering performance.

Unveiling the dual faces of chitosan in anaerobic digestion of waste activated sludge

In this study, the roles of chitosan (CTS) in anaerobic digestion of Waste activated sludge (WAS) were investigated. The results show that the methane production potential of WAS is positively correlated with the CTS content. The presence of 30 g/kg total suspended solids CTS increased the cumulative methane production from 215 ± 1.52 to 272 ± 1.83 mL/g volatile suspended solids. The positively charged amino groups in CTS neutralize the hydroxyl and carboxyl groups of extracellular polymeric substances, which reduces the negative charge on the surface of sludge and promotes sludge agglomeration, thereby inhibiting the release of organic matter. CTS also inhibits hydrolysis and acidification by immobilizing hydrolases and acidulase enzymes. However, CTS flocculates humus to avoid its interference with electron transfer, thereby enhancing the activity of coenzyme F420 and methanogenesis. In addition, CTS increases the abundance of methanogens, which also contributes to methane production.

Solidification effect of river bottom sediments after flocculation via different composite flocculants

The main problem in the reduction of river bottom sediments is to solve the dewatering of the rive sediments. The reduction of river bottom sediments is usually dehydrated by natural air drying and requires more time and economic costs. Different proportions of composite flocculants and curing agents have been developed to the reduction of river bottom sediments according to the requirements of the project. Two or more flocculants were mixed with the rive sediments. Therefore, anionic polyacrylamide (PAM), polyaluminum chloride (PAC), polysilicate aluminum ferric (PSAF), and iron perchloride (IC) were selected for flocculation of river sediments. Through the sedimentation column test, the relationship between sedimentation amount and time was plotted, the turbidity value and pH value of the supernatant filtration supernatant were detected, and the flocculation effect of different flocculants was evaluated to obtain suitable groups of composite flocculants. The optimum ratio of two types of polyacrylamide with a molecular weight of 18 million and 23 million was 3:7. The turbidity of the supernatant of water could well be reduced by adding polysilicate aluminum ferric. Finally, the 6 groups of composite flocculants were determined according to the sedimentation and the turbidity value of the supernatant. The relative water content was maintained at about 60% before and after flocculation. At the same curing age, the compressive strength increased as the amount of curing agent increased after flocculation. At the same curing agent dosage, the overall solidification effect was reduced with increase of curing time after flocculation.

Single-step dynamic dewatering of microalgae from dilute suspensions using flocculant assisted filtration

Background

Dewatering constitutes a major challenge to the production of microalgae, accounting for 20–30% of the product cost. This presents a setback for the applicability of microalgae in the development of several sustainable products. This study presents an investigation into the dynamic dewatering of microalgae in a combined flocculation-filtration process. The effect of process conditions on the performance of 12 flocculants and their mixtures was assessed.

Results

The mechanism of flocculation via the electrostatic path was dominated by charge neutralization and subsequently followed bridging in a ‘sweep flocculation’ process. Cationic polyacrylamide (CPAM) based flocculants recorded the highest biomass retention with PAM1 and PAM2 attaining 99 and 98% retention with flocculant dosages of 10 and 15 mg/L respectively. Polyvinylamine (PVAM) was also found to improve system stability across the pH range 4–10. Alum was observed to be only effective in charge neutralization, bringing the system close to its isoelectric point (IEP). Chemometric analysis using the multi-criteria decision methods, PROMETHEE and GAIA, was applied to provide a sequential performance ranking based on the net outranking flow (ф) from 207 observations. A graphical exploration of the flocculant performance pattern, grouping the observations into clusters in relation to the decision axis (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pi$$\end{document}π), which indicated the weighted resultant of most favorable performance for all criteria was explored.

Conclusion

CPAM based flocculants and their mixtures demonstrated superior performance due to their viscoelastic behaviour under turbulence. The use of PVAM or alum in mixtures with CPAM reduced the required doses of both flocculants, which will provide beneficial financial impact for largescale microalgae dewatering in a flocculant assisted dynamic filtration process. Chemometric analysis based on the physico-chemical properties of the system provides a time saving assessment of performance across several criteria. The study findings provide an important foundation for flocculant assisted dynamic filtration processes.

Microfluidic testing of flocculants for produced water treatment: Comparison with other methodologies

Flocculants are often added during produced water treatment to improve the crude oil droplet growth and separation from the water phase. Prior to use in the field, their performance is tested in laboratory conditions, typically with jar tests that require quite large volumes of sample. In this paper we present a microfluidic method as an alternative to study the efficiency of flocculants on enhancing coalescence between oil droplets. Two crude oil emulsions and four flocculants at different concentrations were tested. The new method is also compared to the more traditional techniques. An anionic flocculant showed the biggest improvement in separation for almost all systems. What is more, marked differences were observed between methods with static (bottle and turbidity tests) and dynamic test conditions (light scattering and microfluidics), where stabilization and dispersion effects were observed for the latter. The microfluidic methodology, with added benefits such as visualization, lower sample volumes and shorter measurement times, yielded similar trends as compared to other techniques. Overall, it was shown that microfluidics is a viable alternative to the standard tests.

Sedimentation of nanoplastics from water with Ca/Al dual flocculants: Characterization, interface reaction, effects of pH and ion ratios

Nanoplastics (NPs), which are broken down from large pieces of plastics and caused water environment pollution, are becoming an emerging environmental problem due to their stable structure, high mobility, and easy interactions with ambient organic compounds. Separation of NPs by flocculation may be an effective approach for remediation of NPs contaminated-water. Aluminum ion has been used as a highly efficient flocculant in sewage treatment, and calcium ion also shows excellent sedimentation performance for impurities under high pH conditions. In this study, composite metal calcium-aluminum (Ca/Al) ions were used as flocculants, achieving a settling efficiency of NPs almost as high as 80%. The effects of pH and Ca/Al flocculant ratios on the zeta potentials, solution stability, as well as sedimentation efficiency of NPs were investigated. Results showed that the crystal formation of Ca/Al flocs increased with pH. The contact and adsorption mechanism of NPs by Ca/Al flocs were confirmed by X-ray diffraction, scanning electron microscope, Fourier Transform Infrared Spectrometer, and X-ray photoelectron spectroscopy. The capture of NPs by Ca/Al flocculants could provide a new insight for the treatment of NPs from aqueous environment.

Negative effect of flocculant (cationic acrylamide) on detectability of the nematode eggs in sewage sludge

The use of sewage sludge in agriculture brings the risk of microbiological and parasitological contamination of soil, ground and surface water, as well as cultivated plants. Therefore prior the application to the soil, sewage sludge must be examined, among others, for the presence of live eggs of intestinal parasites. However, the efficiency of commonly used for this purpose parasitological methods is not satisfactory. This is probably due to the presence of flocculants in the sediments used in the dehydration process. The objective of the study was analysis of the effect of flocculant (cationic acrylamide) on the possibilities of isolation of parasite eggs from dehydrated sewage sludge. For this purpose 10 samples of sewage sludge were prepared: 5 containing flocculant and 5 without flocculant. Samples were tested by flotation method according to Quinn. From sewage sludge free of flocculant, 67.8 eggs were isolated, on average, whereas from sludge containing flocculant - only 2.8 eggs. The experiments confirmed that the isolation of eggs from sewage sludge containing flocculant (cationic acrylamide) is much more difficult than from sludge free from this substance and therefore the simple parasitological methods should not be used to examine the dehydrated sewage sludge.

Inducing flocculation of non-floc-forming Escherichia coli cells

The present article reviews several approaches for inducing flocculation of Escherichia coli cells. The common industrially used bacterium E. coli does not naturally have floc-forming ability. However, there are several approaches to induce flocculation of E. coli cells. One is induction by flocculants-polyvalent inorganic salts, synthetic polymeric flocculants, or bio-based polymeric materials, including polysaccharide derivatives. Another method is the induction of spontaneous flocculation by changing the phenotypes of E. coli cells; several studies have shown that physical treatment or gene modification can endow E. coli cells with floc-forming ability. Coculturing E. coli with other microbes is another approach to induce E. coli flocculation. These approaches have particular advantages and disadvantages, and remain open to clarification of the flocculation mechanisms and improvement of the induction processes. In this review, several approaches to the induction of E. coli flocculation are summarized and discussed. This review will be a useful guide for the future development of methods for the flocculation of non-floc-forming microorganisms.

A novel hydrophobically-modified polyelectrolyte for enhanced dewatering of clay suspension

This work investigates the effect of multifunctional poly (N-isopropyl acrylamide/acrylic acid/N-tert-butylacrylamide) [p(NIPAM-AA-NTBA)] ternary polymer on the sedimentation of kaolin clay - a major fraction of oil sands tailings. A series of linear, uncross-linked p(NIPAM), p(NIPAM/AA), and p(NIPAM/AA/NTBM) were synthesized as random copolymers, where all monomer units were randomly arranged along the polymer backbone and connected by covalent bonds. The ternary copolymer, used as a flocculant, exhibited thermo-sensitivity, anionic nature, and hydrophobic association due to NIPAM, AA, and NTBM, respectively. As the ternary polymer is thermosensitive, it undergoes extended to coil-like conformation, i.e. hydrophilic to hydrophobic transition, above its lower critical solution temperature (LCST). The comonomers NIPAM (above LCST) and NTBM help expel water out of sediments due to their hydrophobicity, while AA promotes charge neutralization of the kaolin clay particles. The effect of number average molecular weight, charge density, and concentration of NTBM on settling behavior of kaolin suspension was examined. Settling test at 50 °C resulted in significantly higher settling rates compared to that at room temperature. Further, the quality of water recovered in each experiment was tested in terms of its turbidity. These results indicate that this novel ternary polymer can be employed to enhance the recovery of water from oil sands tailings containing clays.

New route of chitosan extraction from blue crabs and shrimp shells as flocculants on soybean solutes

The chitosan extracted from blue crabs and shrimp shells using calcium oxide (deproteinization) followed by deacetylation which eliminated the demineralization step to reduce the chemical usage and environmental protection. The extracted chitosan examined the flocculation to soybean solutes. The optical density (OD), solid%, and purity% (carbohydrates/soluble solids) after flocculation were measured. The OD was significantly decreased from 0.76 to 0.16 with blue crabs and 0.06 with shrimp shells chitosan-acetate dosing (0.5 g/L). The removal of about 68 and 66% solids was achieved by the addition of 0.5 g/L chitosan-acetate. The purity% was reached about 80% with blue crabs, and 78% with shrimp shells chitosan-acetate. The results of this study verified that the calcium oxide treatment should remove protein and increase the chitin extraction yield on blue crab and shrimp shells. This new route of chitosan extraction should be a useful method for making flocculants in the soybean solutes.

Degradation of acrylamide by the UV/chlorine advanced oxidation process

The degradation of acrylamide (AA) during UV/chlorine advanced oxidation process (AOP) was investigated in this study. The degradation of AA was negligible during UV irradiation alone. However, AA could be effectively degraded and mineralized during UV/chlorination due to the generation of hydroxyl radicals (OH). The degradation kinetics of AA during UV/chlorination fitted the pseudo-first order kinetics with the rate constant between AA and OH radicals being determined as 2.11 × 10⁹ M^-1 s^-1. The degradation rate and mineralization of AA during UV/chlorination were significantly promoted at acidic conditions as well as increasing chlorine dosage. The volatile degradation products of AA during UV/chlorination were identified using gas chromatography-mass spectrometry and the degradation pathways were then proposed accordingly. The formation of disinfection by-products (DBPs) in Milli-Q water and tap water during UV/chlorination of AA was also investigated. The DBPs included chloroform, dichloroacetonitrile, trichloroacetonitrile, 2,2-dichloroacetamide and 2,2,2-trichloroacetamide. Furthermore, the variations of AA degradation during UV/chlorination in different real water samples were evaluated.

Suspended sludge and biofilm shaped different anammox communities in two pilot-scale one-stage anammox reactors

The abundance and diversity of anammox bacteria was investigated in two pilot-scale integrated fixed-film activated sludge (IFAS) reactors treating high ammonium wastewater. Reactor A was inoculated with nitrifying sludge, while Reactor B was inoculated with suspended anammox sludge with the dominant anammox bacteria of Candidatus 'Kuenenia'. After 180days' operation, the predominate anammox bacteria was Candidatus 'Brocadia' (65%) in the biofilm, while Candidatus 'Kuenenia' (86%) outcompeted with other anammox bacteria in suspended sludge in Reactor A. Candidatus 'Kuenenia' were dominated in suspended sludge through the entire experiment in Reactor B. In contrast, the predominated species shifted from Candidatus 'Kuenenia' (89%) into Candidatus 'Brocadia' (66%) in the biofilm of Reactor B. This study indicated that Candidatus 'Brocadia' preferred to grow in the biofilm, while Candidatus 'Kuenenia' would dominant over other anammox bacteria in the suspended sludge. Further studies are required to identify the internal factors affecting the distribution of anammox bacteria.