Traditional hydrogels with a single-crosslinked network structure suffer from poor stretchability, low sensitivity, and easy contamination, which seriously affect their practical application in the strain sensor field. To overcome these shortcomings, herein, a multiphysical crosslinking strategy (ionic crosslinking and hydrogen bonding) was designed to prepare a hydrogel strain sensor based on chitosan quaternary ammonium salt (HACC)-modified P(AM-co-AA) (acrylamide-co-acrylic acid copolymer) hydrogels. The ionic crosslinking for the double-network P(AM-co-AA)/HACC hydrogels was achieved by an immersion method with Fe3+ as crosslinking sites, which crosslinked with the amino group (-NH2) on HACC and the carboxyl group (-COOH) on P(AM-co-AA) and enabled the hydrogels to recover and reorganize rapidly, resulting in a hydrogel-based strain sensor with excellent tensile stress (3 MPa), elongation (1390%), elastic modulus (0.42 MPa), and toughness (25 MJ/m3). In addition, the prepared hydrogel exhibited high electrical conductivity (21.6 mS/cm) and sensitivity (GF = 5.02 at 0-20% strain, GF = 6.84 at 20-100% strain, and GF = 10.27 at 100-480% strain). Furthermore, the introduction of HACC endowed the hydrogel with excellent antibacterial properties (up to 99.5%) and excellent antibacterial activity against bacteria of three forms, bacilli, cocci, and spores. The flexible, conductive, and antibacterial hydrogel can be applied as a strain sensor for real-time detection of human motions such as joint movement, speech, and respiration, which exhibits a promising application prospect in wearable devices, soft robotic systems, and other fields.
Soft, conductive, and stretchable sensors are highly desirable in many applications, including artificial skin, biomonitoring patches, and so on. Recently, a combination of good electrical and mechanical properties was regarded as the most important evaluation criterion for judging whether hydrogel sensors are suitable for practical applications. Herein, we demonstrate a novel carboxylated carbon nanotube (MWCNT-COOH)-embedded P(AM/LMA)/SiO2@PANI hydrogel. The hydrogel benefits from a double-network structure (hydrogen bond cross-linking and hydrophobic connectivity network) due to the role of MWCNT-COOH and SiO2@PANI as cross-linkers, thus resulting in tough composite hydrogels. The obtained P(AM/LMA)/SiO2@PANI/MWCNT-COOH hydrogels exhibited high tensile strength (1939 kPa), super stretchability (3948.37%), and excellent strain sensitivity (gauge factor = 11.566 at 100-1100% strain). Obviously, MWCNT-COOH not only improved the electrical conductivity but also enhanced the mechanical properties of the hydrogel. Therefore, the integration of MWCNT-COOH and SiO2@PANI-based hydrogel strain sensors will display broad application in sophisticated intelligence, soft robotics, bionic prosthetics, personal health care, and other fields using inexpensive, green, and easily available biomass.
This study demonstrated the feasibility of anaerobic ammonia oxidation (anammox) served as tertiary nitrogen removal process. An upflow fixed-bed reactor (UFBR) pre-inoculated with anammox bacteria (AnAOB) followed an anoxic/oxic (A/O) reactor treating magnetic-coagulation pretreated municipal wastewater. When bypassing 15% of influent into UFBR, UFBR removed 5.37 mg-TN/L contributing to 23.4% on total TN removal, in which the combination of partial nitritation and partial denitrification with anammox was main nitrogen removal pathway. Relatively low concentrations of NH4+-N and anaerobic environment promoted the growth of ammonia oxidizing archaea (AOA) in the inner-layer of biofilm in UFBR. The cooperation of AOA and ammonia-oxidizing bacteria (AOB) with AnAOB was achieved, with AOA, AOB, and AnAOB abundances of 0.01-0.32%, 0.25-0.44%, and 0.77-2.18% on the biofilm, respectively. Metagenomic analysis found that although AOB was the main NH4+-N oxidizer, archaeal amo gene on biofilm increased threefold during 90 days' treatment.
Ammonia , Nitrogen , Anaerobiosis , Bioreactors , Denitrification , Oxidation-Reduction , Wastewater/analysis
Stable production of nitrite is an essential technical challenge for mainstream anaerobic ammonia oxidation (Anammox). Due to difficulties in the stable inhibition of nitrite oxidizing bacteria (NOB) and maintenance of long-term partial nitritation (PN), integrated multiple, rather than a single, controlling strategies were preferred especially in a continuous-flow treatment system. A mathematically model was developed to evaluate effects of integrated multiple-strategies on ammonia oxidizing bacteria (AOB) and NOB. Through experimental study and model simulation, intermittent aeration and low SRT (3.5 d) resulted in unstable nitrite accumulation. Integrated multiple-strategies of intermittent aeration, low SRT (3.5 d) and bioaugmentation achieved nitrite accumulation rate of 81% and NO2--N/NH4+-N ratio in effluent of 1.29, which was preferable for further anammox process. Meanwhile, the richness and diversity of microbial community increased due to the bioaugmentation. The AOB/NOB ratio increased from 13.8 to 34.1 which facilitated nitrite accumulation. In combination with bioaugmentation, the observed growth rates of AOB and NOB increased from -0.0835 and -0.0282 to 0.0434 and 0.0127 d-1, respectively, which promoted AOB outcompeting NOB in the mixed liquid.
Ammonia , Wastewater/analysis , Bioreactors , Nitrites , Nitrogen , Oxidation-Reduction
