filter data on a node using a reference

Hello. I am creating an application with Firebase and Angular 4 and I am not able to create a filter of the information, someone could give me a light on it.

I have a guide list. and I want it to bring me just the data with the local Suzano but how to separate it in the code? the idea is then to create a select of sites.

ngOnInit(){this.GuiaService.getGuias().snapshotChanges().subscribe(item=>{this.guiaList=[];item.forEach(element=>{letguia=element.payload.toJSON();guia["$key"] = element.key;
      this.guiaList.push(guia as Guia);
 console.log(guia)

    });
  });

}