Ammonia removal in the carbon contactor of a hybrid membrane process

Desorption of micropollutant from superfine and normal powdered activated carbon in submerged-membrane system due to influent concentration change in the presence of natural organic matter: Experiments and two-component branched-pore kinetic model

Submerged-membrane hybrid systems (SMHSs) that combine membrane filtration with powdered activated carbon (PAC) take advantage of PAC's ability to adsorb and remove contaminants dissolved in water. However, the risk of contaminant desorption due to temporal changes in the influent concentration of the contaminant has not been thoroughly explored. In this study, we used a SMHS with conventionally-sized PAC or superfine PAC (SPAC) to remove 2-methylisoborneol (MIB), a representative micropollutant, from water containing natural organic matter (NOM), with the goal of elucidating adsorption-desorption phenomena in the SMHS. We found that 20-40% of the MIB that adsorbed on PAC and SPAC while the influent was contaminated with MIB (6 h, contamination period) desorbed to the liquid phase within 6 h from the time that the MIB-containing influent was replaced by MIB-free influent (no-contamination period). The percentage of desorption during the no-contamination period increased with increasing MIB breakthrough concentration during the contamination period. These findings indicate that the PAC/SPAC in the SMHS should be replaced while the breakthrough concentration is low, not only to keep a high removal rate but also to decrease the desorption risk. SPAC is fast in removal by adsorption, but it is also fast in release by desorption. SPAC (median diameter: 0.94 µm) showed almost the same adsorption-desorption kinetics as PAC (12.1 µm) of a double dose. A two-component branched-pore diffusion model combined with an IAST (ideal adsorbed solution theory)-Freundlich isotherm was used to describe and analyze the adsorption-desorption of MIB. The diffusivity of MIB molecules in the pores of the activated carbon particles decreased markedly in a short period of time. This decrease, which was attributed to fouling of the activated carbon in the SMHS by coagulant-treated water containing NOM, not only reduced the rate of MIB removal during the contamination period but also hindered the rate of MIB desorption during the no-contamination period and thus prevented the effluent MIB concentration from becoming high. On the other hand, coagulation did not change the concentration of NOM that competes with MIB for adsorption sites.

Effects of Three Biochars as Adsorbents on Soils Adsorbing Ammonium Nitrogen in Biogas Slurry

The increasing concern of biogas slurry disposal and nitrogen loss in soils has brought back the interest in using biochar as an adsorbent of biogas slurry in soils. Three types of biochars, commercial activated carbon, pyrolysis productions derived from rice husk, and nut shell, were added as adsorbents in two types of soils (sandy and loamy) at solid weight ratio of 5%, 10%, 15%, and 20% to investigate the effects of biochars on soils adsorbing ammonium nitrogen (NH4+-N) in biogas slurry using oscillation method. There was no difference of NH4+-N adsorbability for sand soil and loamy soil. The NH4+-N adsorption capacity of soils increased as the additive biochars increased from 0 to 20%. The smaller particle size of biochars led to the shorter stable adsorption time and the better NH4+-N adsorption capacity. Commercial activated carbon showed the best NH4+-N adsorption capacity in biogas slurry, followed by the nut shell carbon. The rice husk carbon was the worst. The results in this study provide a feasible and cost-effective assessment method of biochars for increasing the NH4+-N adsorption capacity of soils in biogas slurry, as well as good insight into effects of different biochars on improving NH4+-N adsorption capacity of soils.

Performance of biological magnetic powdered activated carbon for drinking water purification

Combining the high adsorption capacity of powdered activated carbon (PAC) with magnetic properties of iron oxide nanoparticles (NPs) leads to a promising composite material, magnetic PAC or MPAC, which can be separated from water using magnetic separators. We propose MPAC as an alternative adsorbent in the biological hybrid membrane process and demonstrate that PAC covered with magnetic NPs is suitable as growth support for heterotrophic and nitrifying bacteria. MPAC with mass fractions of 0; 23; 38 and 54% maghemite was colonized in small bioreactors for over 90 days. Although the bacterial community composition (16s rRNA analysis) was different on MPAC compared to PAC, NPs neither inhibited dissolved organic carbon and ammonia biological removals nor contributed to significant adsorption of these compounds. The same amount of active heterotrophic biomass (48 μg C/cm(3)) developed on MPAC with a mass fraction of 54% NPs as on the non-magnetic PAC control. While X-ray diffraction confirmed that size and type of iron oxides did not change over the study period, a loss in magnetization between 10% and 34% was recorded.