The heat rejected in the condenser is related to the refrigeration capacity and the COP by the following equation:
\[
\text{Heat rejected} = \text{Refrigeration capacity} \times (1 + \frac{1}{\text{COP}}).
\]
Substituting the given values:
\[
\text{Heat rejected} = 150 \times (1 + \frac{1}{10}) = 150 \times 1.1 = 165 \, \text{kJ}.
\]
Thus, the heat rejected by the refrigerant in the condenser is:
\[
\boxed{165 \, \text{kJ}}.
\]