Conventional farmyard manure is produced in smaller farmhouses. In this context, straw is used for the animal beds, and the total solids of these residues range
from 10 to 30 wt%. The farmyard manure digestion needs significantly greater
retention times and can require to perform a pretreatment of the manure when it is
inhomogeneous. Commonly, supplementary operative difficulties, like formation of
scum layer, are observed. Other bedding tools, such as wood chips, are barely
degradable anaerobically.
Garden wastes and agricultural harvest residues can also be utilized as feedstocks
in farm-scale digesters, providing useful fertilizer in form of digestate. This kind of
residues includes leaves, corn stover, clover harvest remainings, stems, spoiled
vegetables or low-quality fruits, silo leachate, and straw.
Corn silage is the energy crop which is mostly used in anaerobic digestion
(Nordberg and Edström 1997). Corn cultivation can be performed also in rotation
with other crops such as triticale or oats. An advantage of silage is represented by the
fact that it can be used and stored over long periods of time.
Wastewaters are produced in the food industries, where important amounts of
agricultural raw materials are treated. Usually, agricultural industrial wastes and
by-products contain proteins, sugars, and fats which have important yields of biogas.
Effluents from the olive oil industry, the dairy industry, fruit juices industry, and
alcohol distilleries can be also used as raw materials for biogas production. Anaerobic digestion can be performed on other industrial effluents, which are not coming
from the agroindustry and also on municipal wastewaters. Table 10.1 shows the most
important characteristics of anaerobic digestion substrates.
10.2 Biogas Raw Materials and Inoculum Characterization
10.2.1 Introduction
The different steps which have to be made to characterize the materials are
shown in Fig. 10.1. The first one is the sampling of the material. The sample is
required to have characteristics that are representative of the bulk materials from
where it has been taken. After sampling, the materials should be properly stored in
the lab and prepared for analysis (e.g., by drying it or milling it). Then classical
analysis comprehends pH measurement, TS and VS measurements, chemical oxygen demand (COD) measurement, total nitrogen measurement, total organic carbon
(TOC) measurement, trace elements, and S and P measurement, alkalinity. The most
important measuring techniques for the above-cited parameters are reported in
(Wellinger et al. 2013), while fundamental knowledge on food analysis is reported
in (Nielsen 2017). As we know, food waste can be a significant raw material for
anaerobic digestion (Bartocci et al. 2020; Liberti et al. 2018); so in this case also the
food composition appears to be important. This is also in light of the fact that biogas
yields can be predicted with modeling tools, such as those developed in (Hafner et al.
2018a) which use as inputs the substrate content of carbohydrates, lipids, and
10 Substrate Characterization in the Anaerobic Digestion Process
309
from 10 to 30 wt%. The farmyard manure digestion needs significantly greater
retention times and can require to perform a pretreatment of the manure when it is
inhomogeneous. Commonly, supplementary operative difficulties, like formation of
scum layer, are observed. Other bedding tools, such as wood chips, are barely
degradable anaerobically.
Garden wastes and agricultural harvest residues can also be utilized as feedstocks
in farm-scale digesters, providing useful fertilizer in form of digestate. This kind of
residues includes leaves, corn stover, clover harvest remainings, stems, spoiled
vegetables or low-quality fruits, silo leachate, and straw.
Corn silage is the energy crop which is mostly used in anaerobic digestion
(Nordberg and Edström 1997). Corn cultivation can be performed also in rotation
with other crops such as triticale or oats. An advantage of silage is represented by the
fact that it can be used and stored over long periods of time.
Wastewaters are produced in the food industries, where important amounts of
agricultural raw materials are treated. Usually, agricultural industrial wastes and
by-products contain proteins, sugars, and fats which have important yields of biogas.
Effluents from the olive oil industry, the dairy industry, fruit juices industry, and
alcohol distilleries can be also used as raw materials for biogas production. Anaerobic digestion can be performed on other industrial effluents, which are not coming
from the agroindustry and also on municipal wastewaters. Table 10.1 shows the most
important characteristics of anaerobic digestion substrates.
10.2 Biogas Raw Materials and Inoculum Characterization
10.2.1 Introduction
The different steps which have to be made to characterize the materials are
shown in Fig. 10.1. The first one is the sampling of the material. The sample is
required to have characteristics that are representative of the bulk materials from
where it has been taken. After sampling, the materials should be properly stored in
the lab and prepared for analysis (e.g., by drying it or milling it). Then classical
analysis comprehends pH measurement, TS and VS measurements, chemical oxygen demand (COD) measurement, total nitrogen measurement, total organic carbon
(TOC) measurement, trace elements, and S and P measurement, alkalinity. The most
important measuring techniques for the above-cited parameters are reported in
(Wellinger et al. 2013), while fundamental knowledge on food analysis is reported
in (Nielsen 2017). As we know, food waste can be a significant raw material for
anaerobic digestion (Bartocci et al. 2020; Liberti et al. 2018); so in this case also the
food composition appears to be important. This is also in light of the fact that biogas
yields can be predicted with modeling tools, such as those developed in (Hafner et al.
2018a) which use as inputs the substrate content of carbohydrates, lipids, and
10 Substrate Characterization in the Anaerobic Digestion Process
309