Datasets on chemical composition and anaerobic digestion of organic fraction of municipal solid waste (OFMSW), digested sewage sludge (inoculum) and ashes from incineration or gasification

This article contains data on the chemical composition and anaerobic digestion of different residue streams including OFMSW, digested sewage sludge, low-carbon (LC) ashes from incineration subdivided into LC coarse and LC fly ash as well as high-carbon (HC) ashes from gasification subdivided into HC reactor and HC fly ash. All materials were collected in accordance to standard procedures in southern Germany. The data presented in this article include (1) dry matter (2) organic dry matter (3) elemental analysis (4) trace elements and (5) cumulative biogas and CH4 yields. Researchers and waste management companies on lab-/pilot-/industrial-scale can rely on the presented data for classification and comparison of biogenic waste streams. For further discussion, please refer to the scientific article entitled “Optimizing anaerobic digestion of organic fraction of municipal solid waste (OFMSW) by using biomass ashes as additives” [1].


a b s t r a c t
This article contains data on the chemical composition and anaerobic digestion of different residue streams including OFMSW, digested sewage sludge, low-carbon (LC) ashes from incineration subdivided into LC coarse and LC fly ash as well as high-carbon (HC) ashes from gasification subdivided into HC reactor and HC fly ash. All materials were collected in accordance to standard procedures in southern Germany. The data presented in this article include (1) dry matter (2) organic dry matter (3) elemental analysis (4) trace elements and (5) cumulative biogas and CH 4 yields. Researchers and waste management companies on lab-/pilot-/industrial-scale can rely on the presented data for classification and comparison of biogenic waste streams. For further discussion, please refer to the scientific article entitled "Optimizing anaero-Value of the data • This data article provides a large characterization of six highly relevant waste types (OFMSW, digested sewage sludge as well as wood ashes from incineration and gasification) and demonstrates the impact of wood ashes on the anaerobic digestion of OFMSW. • This data will be useful for other researchers in the field of bio-and thermo-chemical biomass conversion (comparison, data basis). Managers of biogenic waste streams, biogas plant operators can rely on the data for optimization and identification of waste treatment concepts.  • Researchers and developers in the fields of treatment, recycling and disposal of bio-waste (lab-, pilot-, and industrial-scale) can rely on the presented data for classification and comparison of data and replication/variation of the conducted experiments. • In general, data on the characteristics and bio-chemical treatment of German OFMSW and ashes from wood gasification processes are lacking. Datasets are relevant for the determination of practical application and synergy possibilities of OFMSW, sewage sludge and biomass ashes.

Data description
This Data in Brief article provides the raw data for chemical composition and anaerobic digestion of OFMSW together with digested sewage sludge and low-carbon (LC) ashes from incineration as well as high-carbon (HC) ashes from gasification. All data are presented within this article.  culated according to [ 2 , 3 ]. Values for S can be obtained by using the data from the inductively coupled plasma-optical emission spectroscopy (ICP-OES,  Table 5 -8 . Table 9 -11 present data for the first digestion experiment subdivided into the experimental set-up ( Table 9 ), measured CH 4 concentrations ( Table 10 ) and cumulative gas yields for each time step and digester ( Table 11 ). Table 12 -15 show data for the second digestion experiment subdivided into the experimental set-up ( Table 12 ), measured CH 4 concentrations ( Table 13 ) and cumulative gas yields for each time step and digester ( Tables 14 and 15 ).

Experimental design, materials and methods
Detailed descriptions for all experiments can be found in the original research paper [1] .

Sampling
OFMSW (untreated) was collected at a full-scale thermophilic plug-flow biowaste fermentation plant in southern Germany according to standard procedures defined in the German biowaste ordinance [4] Digested sewage sludge as residue after anaerobic digestion of wastewater (used as inoculum for digestion experiments) was collected at the local municipal sewage Table 4 Raw data and mean values for C, H and N in all materials. For determination of stoichiometric CH 4 yields, S can be calculated by using data from ICP-OES ( Table 8 ) treatment plant (Rottenburg-Kiebingen, Germany) following [5] . LC coarse and LC fly ash from a 50 MW heating plant in southern Germany with a grate fired furnace using a fuel mixture of 50:50 landscape management material and forest residues was provided within another project [6] . HC reactor (minor quantities) and fly ash (major proportion) from a full-scale fixed-bed wood gasifier (Konstanz-Mainau, Germany) fueled with untreated natural wood chips were provided by the plant operator (sampling according to standard procedures). Only HC fly ash was used for digestion experiments because this fraction showed a higher relevance from a disposal perspective. However, both ashes were characterized in order to gain insights in special wood ashes and to compare their TE profiles with OFMSW and sewage sludge. An overview of all materials is provided in Table 1 .

DM, processing and oDM
DM ( Table 2 ) was determined through drying at 105 °C in a drying oven for at least 24 h [7] . The fresh OFMSW sample was manually sorted into fractions to determine the DM content for food waste separately. Before further processing, impurities were removed and the remaining DM was re-combined as well as milled to particle sizes of approximately 1 mm with a cutting mill. The dry sewage sludge was manually crushed in a ceramic mortar (no prior sorting was required). From the dry LC coarse ash, impurities (metals) were removed by manual sorting and sieving with mesh sizes of 16 mm, 8 mm and 3.15 mm. The remaining DM was ground to a particle size of 1 mm by a jaw crusher followed by an orbital mono mill. The dry HC reactor ash was milled by an orbital mono mill to particle size of 1 mm without prior sorting. The particle sizes of HC and LC fly ashes already were below 1 m. Therefore, no further treatment was necessary. oDM ( Table 3 ) was determined by using approximately 1 g of DM in a ceramic crucible by a muffle furnace [8] .

C, H, N, S, O
Elemental analysis (C, H, N) was carried out [9] for all materials containing oDM (sewage sludge, OFMSW and HC ashes; Table 4 ). Approximately 40 mg per sample were pressed into a zinc foil coated tablet. S was not measured simultaneously in favor of the measurement accuracy of C, H and N (S was measured via ICP-OES). The measured values for C, H, N, S and ash were used to determine O contents.

TE
TE (Tables 5, 6, 7, 8) were measured via ICP-OES [10] after digestion in aqua regia. Therefore, 300 mg DM per sample were transferred into 50 mL Teflon vessels and combined with 1 mL H 2 O 2 . Before microwave digestion at 190 °C, 3 mL HNO 3 (69%) and 9 mL HCl (35%) were added. The digested residues were aliquoted to 50 mL with aqua bidest and measured at the ICP-OES system. Solid residues (Si) were separated by a centrifuge before the spectroscopy and their weight was deducted from the sample weight. Therefore, values for Si only represented a partial amount of the total amount (not completely digestible in aqua regia). When evaluating ICP-OES data, all values below the detection limit were equated with this limit. Hence, some of those values might be slightly overestimated as the actual values could be even lower than the detection limit (0 < value < detection limit).

Digestion experiments
The volumetric biogas production was measured using glass manometers whenever the manometer functioning as 1 L gas storage was nearly full, considering the temperature within the digester (2-L insulated glass vessel) and ambient conditions. After several days, the CH 4 concentration was analyzed with a portable biogas analyzer. Specific biogas and CH 4 productions were related to oDM and calculated for standard conditions (1013 hPa, 0 °C, dry gas). Experiments were conducted in two batch test series for 40 days (series 1) and 42 days (series 2) in triplicate and duplicate, respectively (set-ups visible in Table 9 and Table 12 ). All tests were carried out according to [5] .
In series 1, the influence of LC coarse and LC fly ashes on the anaerobic digestion process was determined ( Table 11 ). In series 2, multiple configurations of OFMSW as a baseline feedstock mixed with LC and HC ashes at different ratios were tested ( Table 14 and Table 15 ). Based on the data of series 1, LC coarse ash was used instead of LC fly ash. The remaining oDM content of HC ashes was neglected in calculations as it is considered to be not available for microorganisms. For both series, blind variants were carried out, determining the residual biogas potential of the digested sewage sludge/inoculum.   0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0.11  3  2  4 Table 12 Experimental set-up in test series 2 (operating temperature 35 °C, reactors stirred 60 s/h). oDM contents delivered by ashes ( Table 3 ) were neglected as they were either negligible (LC) or "not available for microorganisms" (HC).

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships, which have, or could be perceived to have, influenced the work reported in this article.