We propose a joint nonlinear electrical equalization approach in coherent optical discrete-Fourier-transform spread orthogonal-frequency-division-multiplexing (DFT-spread-OFDM) systems with polarization division multiplexing (PDM). This method is based on an adaptive Volterra series expansion for nonlinear distortions of two orthogonal polarizations. The nonlinear electrical equalization is validated through numerical simulation of 100-Gb/s quadrature phase shift keying and 200-Gb/s 16 quadrature amplitude modulation PDM DFT-spread-OFDM systems.