A benchmark-based method for evaluating hyperparameter optimization techniques of neural networks for surface water quality prediction

Neural networks(NNs)have been used extensively in surface water prediction tasks due to computing algorithm improvements and data accumulation.An essential step in developing an NN is the hyperparameter selection.In practice,it is common to manually determine hyperparameters in the studies of NNs in water resources tasks.This may result in considerable randomness and require significant computation time;therefore,hyperparameter optimization(HPO)is essential.This study adopted five representatives of the HPO techniques in the surface water quality prediction tasks,including the grid sampling(GS),random search(RS),genetic algorithm(GA),Bayesian optimization(BO)based on the Gaussian process(GP),and the tree Parzen estimator(TPE).For the evaluation of these techniques,this study proposed a method:first,the optimal hyperparameter value sets achieved by GS were regarded as the benchmark;then,the other HPO techniques were evaluated and compared with the benchmark in convergence,optimization orientation,and consistency of the optimized values.The results indicated that the TPE-based BO algorithm was recommended because it yielded stable convergence,reasonable optimization orientation,and the highest consistency rates with the benchmark values.The optimization consistency rates via TPE for the hyperparameters hidden layers,hidden dimension,learning rate,and batch size were 86.7%,73.3%,73.3%,and 80.0%,respectively.Unlike the evaluation of HPO techniques directly based on the prediction performance of the optimized NN in a single HPO test,the proposed benchmark-based HPO evaluation approach is feasible and robust.

Study on the mechanism and reaction characteristics of metal-supported phosphogypsum as oxygen carrier in a chemical looping gasification application

This study aimed to explore the chemical looping gasification(CLG)reaction characteristics of the metal-supported composite phosphogypsum(PG)oxygen carriers(OCs)and the thermodynamic mechanism.The FactSage 7.1 thermodynamic simulation was used to explore the oxygen release and H_(2)S removal mechanisms.The experimental results showed that the syngas yield of CLG with PG-CuFe_(2)O_(4)was more than that with PG-Fe_(2)O_(3)20/CuO40 or PG-Fe_(2)O_(3)30/CuO30 OC at 1023 K when the water vapor content was 0.3.Furthermore,the maximum syngas yield of the CO selectivity was 70.3% and of the CO_(2)selectivity was 23.8%.The H_(2)/CO value was 0.78,and the highest carbon conversion efficiency was 91.9% in PG-CuFe_(2)O_(4)at the gasification temperature of 1073 K.The metal-supported PG composite oxygen carrier was proved not only as an oxygen carrier to participate in the preparation of syngas but also as a catalyst to catalyze coal gasification reactions.Furthermore,both the experimental results and FactSage 7.1 thermodynamic analysis revealed that the trapping mechanism of H_(2)S by composite OCs was as follows:CuO first lost lattice oxygen as an oxygen carrier to generate Cu_(2)O,which,in turn,reacted with H_(2)S to generate Cu_(2)S.This study provided efficient guidance and reference for OC design in CLG.

Inactivation and subsequent reactivation of Aspergillus species by the combination of UV and monochloramine: Comparisons with UV/chlorine

Ultraviolet(UV)/monochloramine(NHCl) as an advanced oxidation process was firstly applied for Aspergillus spores inactivation. This study aims to: i) clarify the inactivation and photoreactivation characteristics of UV/NHCl process, ii) compared with UV/Clin inactivation efficiency, photoreactivation and energy consumption. The results illustrated that UV/NHCl showed better inactivation efficiency than that of UV alone and UV/Cl, and could effectively control the photoreactivation. For instance, the inactivation rates for Aspergillus flavus, Aspergillus niger and Aspergillus fumigatus in the processes of UV/NHCl(2.0 mg/L) was 0.034, 0.030 and 0.061 cm^(2)/m J), respectively, which were higher than that of UV alone(0.027, 0.026 and 0.024 cm^(2)/m J) and UV/Cl(0.023, 0.026 and 0.031 cm^(2)/m J). However, there was no synergistic effect for Aspergillus flavus and Aspergillus fumigatus. As for Aspergillus niger, the best synergistic effect can reach 1.86-log 10. This may be due to their different resistance to disinfectants, which were related to the size, an outer layer of rodlets(hydrophobins) and pigments. After UV/NHCl inactivation, the degree of cell membrane damage and intracellular reactive oxygen species were higher than that of UV alone. UV/NHCl had the advantages of high inactivation efficiency and inhibition of photoreactivation, which provides a new entry point for the disinfection of waterborne fungi.

Valorisation of alum sludge to produce green and durable mortar

Alum sludge is a typical by-product of drinking water treatment processes.Most sludge is disposed of at landfill sites,and such a disposal method may cause significant environmental concern due to its vast amount.This paper assessed the feasibility of reusing sludge as a supplementary cementitious material,which could efficiently exhaust stockpiled sludge.Specifically,the pozzolanic reactivity of sludge at different temperatures,the reaction mechanism of the sludge-cement binder,and the resistance of sludge-derived mortar to microbially induced corrosion were investigated.The obtained results indicated that 800℃ was the optimal calcination temperature for sludge.Mortar containing sludge up to 30%by weight showed comparable physical properties at a curing age of 90 days.Mortar with 10%cement replaced by sludge can significantly improve the resistance to biogenic corrosion due to the formation of Al-bearing phases with high resistance to acidic media,e.g.,Ca_(4)Al_(2)O_(7)·xH_(2)O and strätlingite.

New insight into scale inhibition during tea brewing: Ca^(2+)/Mg^(2+) complexing and alkalinity consumption

Scale not only affects the taste and color ofwater,but also increases the risks of osteoporosis and cardiovascular diseases associated with drinking it.As a popular beverage,tea is rich many substances that have considerable potential for scale inhibition,including protein,tea polyphenols and organic acids.In this study,the effect of tea brewing on scale formationwas explored.It was found that the proteins,catechins and organic acids in tea leaves could be released when the green tea was brewed in water with sufficient hardness and alkalinity.The tea-released protein was able to provide carboxyl groups to chelate with calcium ions(Ca^(2+)),preventing the Ca^(2+)from reacting with the carbonate ions(CO_(3)^(2-)).The B rings of catechins were another important structure in the complexation of Ca^(2+)and magnesium ions(Mg2+).The carboxyl and hydroxyl groups on the organic acids was able to form fivemembered chelating rings with Ca^(2+)and Mg^(2+),resulting in a significant decrease in Ca^(2+)from 100.0 to 60.0 mg/L.Additionally,the hydrogen ions(H^(+))provided by the organic acids consumed and decreased the alkalinity of the water from 250.0 to 131.4 mg/L,leading to a remarkable reduction in pH from 8.93 to 7.73.It further prevented the bicarbonate(HCO_(3)^(-))from producing CO_(3)^(2−)when the water was heated.The reaction of the tea constituents with the hardness and alkalinity inhibited the formation of scale,leading to a significant decrease in turbidity from 10.6 to 1.4 NTU.Overall,this study provides information to help build towards an understanding of the scale inhibition properties of tea and the prospects of tea for anti-scaling in industrial applications.

A novel colorimetric method for field arsenic speciation analysis

Accurate on-site determination of arsenic （As） concentration as well as its speciation presents a great environmental challenge especially to developing countries. To meet the need of routine field monitoring, we developed a rapid colorimetric method with a wide dynamic detection range and high precision. The novel application of KMnO4 and CHaN2S as effective As（III） oxidant and As（V） reductant, respectively, in the formation of molybdenum blue complexes enabled the differentiation of As（III） and As（V）. The detection limit of the method was 8 ~tg/L with a linear range （R2 = 0.998） of four orders of magnitude in total As concentrations. The As speciation in groundwater samples determined with the colorimetric method in the field were consistent with the results using the high performance liquid chromatography atomic fluorescence spectrometry, as evidenced by a linear correlation in paired analysis with a slope of 0.9990- 0.9997 （p 〈 0.0001, n = 28）. The recovery of 96%-116% for total As, 85%-122% for As（III）, and 88%-127% for As（V） were achieved for groundwater samples with a total As concentration range 100-800 μg/L. The colorimetric result showed that 3.61 g/L As（III） existed as the only As species in a real industrial wastewater, which was in good agreement with the HPLC-AFS result of 3.56 g/L As（Ⅲ）. No interference with the color development was observed in the presence of sulfate, phosphate, silicate, humic acid, and heavy metals from complex water matrix. This accurate, sensitive, and easy-to-use method is especially suitable for field As determination.

Algae functional group characteristics in reservoirs and lakes with different trophic levels in northwestern semi-humid and semi-arid regions in China

In order to study the differences in algae species and their biomass in water bodies in a region, three reservoirs and two lakes at the center of Guanzhong Plain were chosen to identify algae functional groups, measure biomass, and assess water quality, from January2013 to December 2014. The water bodies represented different trophic levels： one oligotrophic, three mesotrophic, and one eutrophic. Based on the Reynolds’ functional groups, they had 10 groups in common—B, P, D, X1, M, MP, F, S1, J, and G, but the algae biomasses and proportions were different. In the oligotrophic reservoir, functional group B reached a peak biomass of 576 × 104 L-1, which accounted for 31.27%. In the eutrophic lake,functional group D reached a peak biomass of 3227 × 104 L-1, which accounted for only13.38%. When samples collected from other water bodies with similar trophic levels were compared, we found differences in the algae species functional groups. The potential reasons for the differences in algae functional group characteristics in the different water bodies in the region were water temperature and nutritional states.

New method for efficient control of hydrogen sulfide and methane in gravity sewers:Combination of NaOH and nitrite

An innovative treatment method by the combination of NaOH and nitrite is proposed for controlling hydrogen sulfide and methane in gravity sewers and overcome the drawbacks of the conventional single chemical treatment.Four reactors simulating gravity sewers were set up to assess the effectiveness of the proposed method.Findings demonstrated hydrogen sulfide and methane reductions of about 96.01%and 91.49%,respectively,by the combined addition of NaOH and nitrite.The consumption of NaNO_(2) decreased by 42.90%,and the consumption rate of NaOH also showed a downward trend.Compared with a single application of NaNO_(2),the C/N ratio of wastewater was increased to about 0.61 mg COD/mg N.The greenhouse effect of intermediate N2O and residual methane was about 48.80 gCO_(2)/m^(3),which is far lower than that of methane without control(260 gCO_(2)/m^(3)).Biofilm was destroyed to prevent it from entering the sewage by the chemical additives,which reduced the biomass and inhibited the recovery of biofilm activity to prolong the control time.The sulfide production rate and sulfate reduction rate were reduced by 92.32%and 85.28%,respectively.Compared with conventional control methods,the cost of this new method was only 3.92×10^(−3)$/m^(3),which is potentially a cost-effective strategy for sulfide and methane control in gravity sewers.