Enhancing aerobic digestion of full-scale waste activated sludge using free nitrous acid pre-treatment

Aerobic digestion is one of the mainstream technologies for waste activated sludge (WAS) reduction and stabilization prior to disposal, but its effectiveness is limited by the poor degradation of WAS. This study presents a novel strategy based on free nitrous acid (FNA i.e. HNO2) pre-treatment to enhance full-scale WAS degradation in aerobic digestion. The full-scale WAS was subject to FNA treatment at 2.0 mg HNO2-N per L for 24 h. The degradation of the FNA-treated WAS was then compared to that of the same WAS without FNA pre-treatment by aerobically digesting the WAS with a full-scale activated sludge for 14 days. Approximately 50% of the FNA-treated WAS was degraded during the 14 day aerobic digestion compared to 32% achieved with the untreated WAS. The inorganic nitrogen production (originating from breakdown of WAS) from the FNA-treated WAS was 43 mg N per g of mixed liquor volatile suspended solids (MLVSS) in the 14 day aerobic digestion, whereas its production from the untreated WAS was only 29 mg N per g of MLVSS, confirming the effectiveness of the FNA pre-treatment in enhancing aerobic digestion of full-scale WAS. Economic analysis showed that the FNA pre-treatment method was economically attractive, saving a cost of %-15 500-64 500 per year depending on WAS disposal cost in a treatment plant with a population equivalent of 80 000

Inactivation and adaptation of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria when exposed to free nitrous acid

Inactivation and adaptation of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) to free nitrous acid (FNA) was investigated. Batch test results showed that AOB and NOB were inactivated when treated with FNA. After an 85-day operating period, AOB in a continuous pre-denitrification reactor did not adapt to the FNA that was applied to treat some of the return activated sludge. In contrast, NOB did adapt to FNA. NOB activity in the seed sludge was only 11% of the original activity after FNA batch treatment, at 0.75 mg HNO2-N/L. NOB activity in the pre-denitrification reactor was not affected after being exposed to this FNA level. Nitrosomonas was the dominant AOB before and after long-term FNA treatment. However, dominant NOB changed from Nitrospira to Candidatus Nitrotoga, a novel NOB genus, after long-term FNA treatment. This adaptation of NOB to FNA may be due to the shift in NOB population makeup

Impact of LHCb 13 TeV WW and ZZ pseudo-data on the Parton Distribution Functions

We study the potential of the LHCb 13 TeV single $W^{\pm}$ and $Z$ boson pseudo-data for constraining the parton distribution functions (PDFs) of the proton. As an example, we demonstrate the sensitivity of the LHCb 13 TeV data, collected with integrated luminosities of 5 fb$^{-1}$ and 300 fb$^{-1}$, to reducing the PDF uncertainty bands of the CT14HERA2 PDFs, using the error PDF updating package {\sc ePump}. The sensitivities of various experimental observables are compared. Generally, sizable reductions in PDF uncertainties can be observed in the 300 fb$^{-1}$ data sample, particularly in the small-$x$ region. The double-differential cross section measurement of $Z$ boson $p_T$ and rapidity can greatly reduce the uncertainty bands of $u$ and $d$ quarks in almost the whole $x$ range, as compared to various single observable measurements.Comment: 25 pages, 13 figure

Free nitrous acid breaks down extracellular polymeric substances in waste activated sludge

Free nitrous acid (FNA) has been demonstrated to be effective in enhancing the degradability of waste activated sludge (WAS). Considering that extracellular polymeric substances (EPS) are a major component in sludge flocs, the chemical breakdown of EPS components by FNA has been hypothesized to account for the improvement of sludge biodegradability in addition to enhanced cell lysis. EPS extracted from WAS was treated with FNA at 2.0 mg HNO2-N per L (260 mg NO2--N per L and pH 5.5). The molecular weight distribution of EPS showed the breakdown of macromolecules into smaller molecules. The chemical structure analysis of EPS using Fourier transform infrared spectroscopy ascribed the breakdown to FNA-induced deamination of proteins, amino sugars and nucleic acids, implying that the main targets of FNA in EPS are protein-like substances. Particle size distribution analysis on the original WAS with the same FNA treatment revealed that FNA treatment of sludge significantly reduces the flocs sizes, which supported that FNA breaks down EPS in activated sludge flocs

Heterotrophic denitrification plays an important role in N2O production from nitritation reactors treating anaerobic sludge digestion liquor

Nitrous oxide (N2O) emissions from nitritation reactors receiving real anaerobic sludge digestion liquor have been reported to be substantially higher than those from reactors receiving synthetic digestion liquor. This study aims to identify the causes for the difference, and to develop strategies to reduce N2O emissions from reactors treating real digestion liquor. Two sequencing batch reactors (SBRs) performing nitritation, fed with real (SBR-R) and synthetic (SBR-S) digestion liquors, respectively, were employed. The N2O emission factors for SBR-R and SBR-S were determined to be 3.12% and 0.80% of the NH4+-N oxidized, respectively. Heterotrophic denitrification supported by the organic carbon present in the real digestion liquor was found to be the key contributor to the higher N2O emission from SBR-R. Heterotrophic nitrite reduction likely stopped at N2O (rather than N2), with a hypothesised cause being free nitrous acid inhibition. This implies that all nitrite reduced by heterotrophic bacteria was converted to and emitted as N2O. Increasing dissolved oxygen (DO) concentration from 0.5 to 1.0mg/L, or above, decreased aerobic N2O production from 2.0% to 0.5% in SBR-R, whereas aerobic N2O production in SBR-S remained almost unchanged (at approximately 0.5%). We hypothesised that DO at 1mg/L or above suppressed heterotrophic nitrite reduction thus reduced aerobic heterotrophic N2O production. We recommend that DO in a nitritation system receiving anaerobic sludge digestion liquor should be maintained at approximately 1mg/L to minimise N2O emission

The Application of Solar Indirect System in Passive House in Cold Region and Severe Cold Region of CHINA

AbstractThis paper, the future developing prospect of application of passive house in China was provided,solar indirect system combined with fresh air ventilation system with heat recovery was used in designing to provide heat to meet fresh air load in the passive house, taking the Xining city as an example. The aperture areas of solar collector in different conditions were calculated by changing the influence factors such as the tilt angle of the collector and the solar fraction. This paper analyzed the relationship of the solar collector aperture area with the tilt angle of the collector and the solar fraction. On the basis of the analysis, it is safe to draw a conclusion that the program of using solar indirect system combined with fresh air ventilation system with heat recovery in passive house in cold region and severe cold region of China is economically feasible

Producing free nitrous acid - A green and renewable biocidal agent - From anaerobic digester liquor

Recent studies have shown that free nitrous acid (FNA) at parts per million is strongly biocidal to a broad range of microorganisms involved in wastewater management. Applications have been developed, where FNA is used to deactivate anaerobic sewer biofilms thus suppressing sulfide and methane production in sewers, or to lyse secondary sludge resulting in reduced sludge production and enhanced biogas production. This study examines the feasibility of producing FNA from a waste stream namely the anaerobic sludge digestion liquor, thus providing a source of FNA for the above applications within wastewater systems. Complete nitritation was achieved in a lab scale sequencing batch reactor (SBR) treating reject wastewater. Under stable operation, the system sustained more than 90% conversion of the 1.0 and 0.8g NH4 +-N/L contained in the synthetic and real digester liquor, respectively, to nitrite. Each liter of this nitrite rich effluent could be acidified to pH 2 with only 66 mmol of H+, due to the low level of alkalinity in the effluent. This converts almost all of the nitrite to FNA providing an ample source of FNA for sewer and sludge pretreatment applications. Despite the high nitrite concentration in the reactor, minimal N2O was produced with an emission factor of 0.08% of the ammonium nitrogen converted. Finally, an economical assessment of a theoretical full-scale installation for FNA production was conducted and compared with the costs of producing this FNA from a commercial nitrite supply