FREMONT, Nebraska — The remains of two girls and a relative who were killed in a massive explosion at a Nebraska biofuel plant were recovered Wednesday after crews battled smoldering wreckage and an unstable building for more than 24 hours. Fremont Mayor Joey Spellerberg said earlier at a news conference that the children were at the Horizon Biofuels plant ahead of a doctor’s appointment. …The plant makes animal bedding and wood pellets for heating and smoking food, using tons of wood waste. Spellerberg said authorities believe Tuesday’s blast was likely a wood dust explosion in the tall elevator tower. …The company has 10 employees, according to the Nebraska Manufacturing Extension Partnership.