# Insights into PCDD/Fs and PAHs in Biomass Boilers Envisaging Risks of Ash Use as Fertilizers
## 3 Experimental Part  
### Materials and Methods  
Experiments were performed within the scope of a project dedicated to the study of biomass ash quality in view of its application in soils. Four boilers of biomass power stations located in Portugal, near the Atlantic coast, were involved. Three boilers consist of Bubbling Fluidized Bed systems (BFB) located in pulp & paper plants. They consume mainly forest biomass residues (FBR), composed of shredded bark and branches of eucalyptus trees used for pulp making and paper sludge (from primary and secondary wastewater treatment). Variable quantities of other forest residues are used, such as pine remains and weed trees. Some of these boilers are allowed to consume till 10% of MSW and other non-contaminated biomass residues. The fourth boiler is a grate furnace (GF) also consuming FBR, pine and eucalyptus residues from wildfires and plague control, and occasionally agricultural residues from olive oil production or wood industries. All boilers are equipped with ESPs to reduce particulate emissions. The study was developed during 2011-2013 under the normal and steady operation of boilers. Sampling campaigns lasted a year, during which four or five biomass composed samples were collected, by increments, in the conveyer belts of the furnace's feeding systems of each boiler. In total, 18 biomass samples were prepared for individual chemical analysis; the extraneous mineral matter (rocks, sand, and loosely attached soil) was previously separated by sieving below 2 mm and manual separation. The samples were dried and milled below 0.63 mm and the analyses were performed according to ASTM, EPA, ISO and CEN/TS standards for biomass analysis or equivalent methods in LNEG installations, as described previously [230]. For PCDD/Fs analyses, representative biomass blends of each boiler, containing the individual samples collected for one year, were prepared. Also, sludge from pulp & paper wastewater treatment (mix of 70% primary and 30% secondary sludge) was analyzed for chemical composition and PCDD/Fs. A soil sample collected in the experimental forest campus, used in the project to test ash fertilization, was also tested for PCDD/Fs. Ash samples were collected in the four boilers: monthly in BFB1 and BFB3 (\(n=12\)), bimonthly in GF (\(n=6\)) and three times a year in BFB4 (\(n=4\)). The nature of ash streams collected varies depending on the furnace assembling, ash removal systems installed and ash management strategy. In each boiler, the ash flows are combined in two streams; bottom ash (BA) and fly ash (FA), as described in Table 3. In unit BFB4, BA includes bottom bed ashes and ashes from the economizer (EC), superheater (SH), thus, FABFB4 corresponds only to fly ash from the ESP. For the other three units, BA corresponds only to bottom or grate ashes, therefore, FA are mixes of EC, SH, and ESP ashes. In total, 60 ash samples (30 BA and 30 FA) were prepared for individually chemical analysis. The extraneous matter, above 2 mm, was sieved out. Samples were analyzed following adequate ASTM, EPA, ISO and CEN/TS standards or equivalent methods in LNEG, as described previously [56; 230]. For each boiler, representative ash blends (4 BA and 4 FA) containing the ashes collected during a year were prepared for PCDD/Fs and PAHs analysis. The bulk chemical analysis, leachability, TEQs and \(\Sigma\)PAHs of some of these ash blends were previously presented [56] but additional and more detailed results are provided herein. The PCDD/Fs and PAHs analysis were subcontracted to the Portuguese Reference Laboratory of Agencia Portuguesa do Ambient (APA). PAHs were analyzed using an APA internal method (MMA 98 - SPE-SOX, HPLC/DAD-FLD), based on US EPA method 550.1. PCDD/Fs were analyzed using an APA internal method (MMA 123-LLE-SOX, HRGC/HRMS), based on US EPA method 1613. The lists of 17 PCDD/Fs and 16 PAHs analyzed correspond to those normally used for environmental risk assessment, as presented in Tables 1 and 2.