Abstract:
The goal of the present study was to evaluate the immobilization and retention of caffeine (CFN) in soil and the
influence of biochar for the CFN transport in agricultural soil. The biochar was produced from the Ulva reticulata
seaweed biomass (ULBC) under the slow-pyrolysis with a heating rate of 7 ◦C/min at 500 ◦C and characterized
using XRD and FTIR. The CFN retention and transport abilities in loamy sand and ULBC amended (2.5%) soil
were evaluated under various pH values range of 3–10 and at various CFN concentrations using batch and
column experiments. The surface orientation of ULBC was portrayed as the randomized distribution of hetero
and homogeneous nature. The highest retention capacity (40 μg/g) was obtained at pH 4.0. Soil amendment with
ULBC shows a higher retention affinity towards CFN, of up to 150 μg/g than soil, with minimal pH dependence.
The maximum CFN adsorption capacities of soil and amended soils were 420 and 820 μg/g, respectively, based
on the Langmuir model. Batch experiments suggested the adsorption of CFN by the biochar amended loamy soil
is governed by the electrostatic attraction. The column experiment data demonstrated a high transport potential
of CFN in the loamy sand; however, a strong cumulative reduction of transport (58%) was observed with the
application of ULBC into the loamy sand. Thus, the addition of seaweed biochar as an amendment in soils with
biosolids and wastewater irrigation may reduce the mobilization of CFN to the aquatic system and possibly
reduce plant uptake.
