  We present detailed implementations of (a) binary stellar evolution (using
binary_c) and (b) dust production and destruction into the cosmological
semi-analytic galaxy evolution simulation, L-Galaxies. This new version of
L-Galaxies is compared to a version assuming only single stars and to global
and spatially-resolved observational data across a range of redshifts ($z$). We
find that binaries have a negligible impact on the stellar masses, gas masses,
and star formation rates of galaxies only if the total mass ejected by massive
stars is unchanged. This is because massive stars determine the strength of
supernova (SN) feedback, which in turn regulates galaxy growth. Binary effects,
such as common envelope ejection and novae, affect carbon and nitrogen
enrichment in galaxies, however heavier alpha elements are more affected by the
choice of SN and wind yields. Unlike many other simulations, the new L-Galaxies
reproduces observed dust-to-metal (DTM) and dust-to-gas (DTG) ratios at
$z\sim{}0-4$. This is mainly due to shorter dust accretion timescales in
dust-rich environments. However, dust masses are under-predicted at $z>4$,
highlighting the need for enhanced dust production at early times in
simulations, possibly accompanied by increased star formation. On sub-galactic
scales, there is very good agreement between L-Galaxies and observed dust and
metal radial profiles at $z=0$. A drop in DTM ratio is also found in diffuse,
low-metallicity regions, contradicting the assumption of a universal value. We
hope that this work serves as a useful template for binary stellar evolution
implementations in other cosmological simulations in future.
