Study on dynamic sorption characteristics of modified biochars for ammonium in biogas slurry

The objective of this study was to investigate the relationship between ammonium(NH^(+)_(4)-N)dynamic sorption capacity and physicochemical properties of modified biochars.Biochars,producing from three species of agricultural wastes of cornstalk(A),corncob(B)and sawdust(C)at 550°C,600°C and 650°C,were modified by four methods of NaOH plus microwave(NaM),KOH(K),FeCl 3(Fe)and HNO 3(H).The static and dynamic adsorption experiments were conducted to investigate sorption characteristics of modified biochars on NH^(+)_(4)-N in slurry of piggery manure anaerobic digestate.Four modified biochars with better NH^(+)_(4)-N adsorption rates were selected through static kinetics adsorption tests,which showed that chemical reactions might have occurred during the NH^(+)_(4)-N sorption process and the maximum NH^(+)_(4)-N removal rates of B-550-Fe,A-550-NaM,A-550-K and C-600-NaM were 66.64%,57.50%,52.39%and 45.20%,respectively.The dynamic adsorption column experiment was conducted in a three-stage adsorption column packed with the selected three modified biochars.NH^(+)_(4)-N dynamic adsorption depended on the slurry inflow flow rate,the type of biochar and the depth of packed biochar.The optimal adsorption process was elected by the method of orthogonal experiment.The data showed that using deeper packed biochar and applying lower flow rates could be a better strategy to increase NH^(+)_(4)-N adsorption.The maximum NH^(+)_(4)-N removal rate in the slurry could reach 85.60%in the three-stage adsorption process.It concluded that NH^(+)_(4)-N adsorption in three-stage adsorption process could be an effective method to recover nitrogen from piggery manure anaerobic digestate.

Sorption of Heavy Metal and Organic Pollutants on Modified Soils

Sorption characteristics of both an organic pollutant (phenol) and a heavy metal (cadmium ion) on the clay layer of a Lou soil (Eum-orthic Anthrosol in Chinese Soil Taxonomy) along with the sorption mechanism were investigated using three soil treatments: modification with a cationic surfactant cetyltrimethylammonium bromide added at an amount equivalent to 50% and 100% of the soil CEC (50%CB and 100%CB), modification with an amphoteric surface-modifying agent dodecyldimethylbetaine (commercially known as BS-12) added at an amount equivalent to 50% and 100% of the soil CEC (50% BS and 100%BS), and an unmodified control (CK). Results showed that the BS soil treatments increased sorption of both the heavy metal Cd2+ and the organic pollutant phenol. The equilibrium sorption amount of Cd2+ decreased in the order: 50%BS > 100%BS > CK > 50%CB > 100%CB, with the BS soil treatments being about 1.3 to 1.8 times higher and the CB soil treatments about 23% to 41% lower than CK. Both the single-site and two-site Langmuir models could be applied to describe the sorption of Cd2+ in each soil treatment. The equilibrium sorption amount of phenol on the soil samples decreased in the order: 100%CB > 50%CB > 100%BS > 50%BS > CK, with the CB soil treatments being 41.0 to 79.6 times higher and the BS soil treatments 4.0 to 8.3 times higher than CK. The Freundlich equation could also be used to describe the sorption characteristics of phenol. In the BS soil treatments, both an organophobic long carbon chain and hydrophilic charged groups resulted in a relatively strong sorption ability for both heavy metals and organic pollutants. In addition, the sorption ratio K, the ratio of phenol sorption amount of the modified soil to that of CK, increased initially and decreased later with the amount of phenol added, and the critical sorption ratio KC, the peak value of the sorption ratio curve plotted against the added phenol concentration, was a good index for evaluating the sorption ability of phenol in the soil.