**1. Introduction (Composting)**

The composting technique emerged around the year 1920, when a researcher named Albert Howard developed the process in India [1]. This process happens naturally next to the environment, where the biological degradation of the compounds occurs [2], this technique can still be characterized as a process of treatment of different types of residues and origins, among them (urban, industrial, forestry and agricultural), where a diverse population of microorganisms (bacteria, fungi) act [3].

**Figure 1.** *Composting phases according to the temperature in the system. Source: Adapted from [3].*

During the composting process, four fundamental stages for the biodegradation of the compounds occur: initial mesophilic phase, thermophilic, mesophilic cooling and maturation. In the initial phase, mesophilic, the decomposition process accelerated by the gradual increase of existing microorganisms, as well as the increase in temperature. In the thermophilic phase, the temperature of the composting system can reach more than 60°C, resulting from the action and thermophilic microorganisms, generating heat and water vapor. In the mesophilic phase of cooling, the most resistant compounds degraded by mesophilic microorganisms, which after this degradation eventually decrease their activity. Finally, the maturation phase, where the decomposition is low or zero and where the humid are released, generating by end, a stabilized compound [1]. The temperature profile during the composting phases are showing in **Figure 1**.

During the composting phases, CO2 detachment and heat release occur in the composted material (mesophilic phase), reaching the temperature peaks, where the vapor (thermophilic phase) is generated, which also contributes to inertization in the system, all based on the metabolism of microorganisms [2].

Composting has several benefits for the management of waste produced by pig producers, as it can eliminate up to 90% of the effluent volume [4]. The process also has numerous advantages: minimizes the generation of greenhouse gases, reduces the proliferation of vectors, reduces odors, has environmental technical feasibility, elimination of costs for disposal and transport of waste, technical feasibility to expand the current pig production systems [2–5].

#### **2. Physical-chemical composting parameters**

For the composting process to succeed, some aspects such as heat transfer, airflow, steam and finally moisture balance must observed [6]. The main parameters to be evaluated during the composting process are: oxygen/aesthesia; pH; Moisture content; Temperature; C/N ratio, in addition to the presence of microorganisms [6].

Oxygen is directly interconnected with microbial activity, due to the composting process, being aerobic. The obtaining of oxygen from the composting system can be obtained by mechanical, physical or even forced aeration [7]. Its consumption and supply is tied, the humidity of the composting system, having optimum humidity in the range of 55%. The higher the microbial activity, the higher the demand for oxygen and the lower the humidity in the composting system [7]. Also for the author, systems with humidity below 40%, can inhibit the activity of bacteria, predominantly the higher activity of fungi.

**241**

*Composting of Pig Effluent as a Proposal for the Treatment of Veterinary Drugs*

The aeration has equal importance in the process, because with greater revolving and aeration of the system, the rate of decomposition of organic matter is increased. In his experiment of mechanized composting [5], he made the aeration during the injection of effluents in the trees and after 2 days, where he made only the revolving

The state of organic matter decomposition can be measured from the hydrogenic potential (pH) found in the composting system, because for each phase of the process, the pH variation will occur. The initial pH values can be in the order of 4–5 [7], this due to the release of minerals acids and carbonic gas, where at this time the bacteria acidophilus and fungi act in the decomposition of cellulose [3]. Subsequently, the pH can reach values between 7 and 12, due to the formation of organic acids by

alkalophiles bacteria [7], when there is stabilization of the compound [3].

With the ease of measuring throughout the process, the temperature profile plays a crucial role in composting. The temperature can range from 10–70°C, mesophilic phase and thermophilic respectively [3]. Its elevation and decrease linked with humidity and microbial activity, as demonstrated in the temperature profile in

Another important role of this parameter is the inertization and maturation of the compound over time. Pathogen microorganisms have their inactivation from three days at temperatures higher than 55°C [8], but in composting cells where revolving often occurs; the minimum is 15 days with temperatures above 55°C [4]. Aspects such as raw material, composting system configuration, presence of microorganisms, moisture, oxygen, directly affect temperature. Still the temperature can define the amount of revolving of the composting system. In his work [1], he observed the temperature variation in a process of composting of cattle slaughter residues, and in another study, [4], in a process of composting of pig effluents; both studies presented maximum temperatures did not exceed 55°C. In relation to **Figure 3(a)**, it is also noted that when revolving the composting system, the internal temperature increases significantly. Temperature profiles vary from research to research, [5] observed 72°C in the composting system at 22 days of experiment, [2], observed values not exceeding 52°C, already [9], obtained the maximum tempera-

To prepare the composting system it is necessary to note the Carbon/Nitrogen ratio. Both compounds are important in the process, where carbon acts as an energy source and nitrogen as a respirometric source of microorganisms [3], also acting, in cell growth, formation of proteins, amino acids and nucleic acids [2]. The C/N ratio has been observed by several authors [1–4, 6, 9–11], who evaluated that this ratio should not exceed 30/1 in the initial phase, because in high relationships, the degradation of the compounds is delayed, already at the end, when the compound is matured, the ratio may reach 10/1. In this process, much of the carbon is released into the atmosphere in the form of CO2 [6], and nitrogen can be released, when the

ratio is low, in the form of ammonia, characterizing bad odor [2].

Moisture in the composting system is of fundamental importance, being correlated with the rate of decomposition of organic matter by aerobic microorganisms. As already mentioned above, the ideal rate varies between 50% [3], and 55% [7]. Its control can was established by revolving, because at high humidity, anaerobiosis may occur in the system [3]. This, can also was controlled by the relationship between effluent injection and the amount of dry mass (DM). The author [5] used an initial rate of 1.47 liters of scum per kg (DM) in the first days up to a rate of 0.21 liters of scum per kg (DM) at the end of the experiment. Other aspects need observed, which are the phases of the composting process, mesophilic and thermophilic phase, both related to the elevation and decrease of temperature and water

*DOI: http://dx.doi.org/10.5772/intechopen.94758*

of organic matter.

evaporation.

**Figure 1**.

ture of 61°C.

The aeration has equal importance in the process, because with greater revolving and aeration of the system, the rate of decomposition of organic matter is increased. In his experiment of mechanized composting [5], he made the aeration during the injection of effluents in the trees and after 2 days, where he made only the revolving of organic matter.

Moisture in the composting system is of fundamental importance, being correlated with the rate of decomposition of organic matter by aerobic microorganisms. As already mentioned above, the ideal rate varies between 50% [3], and 55% [7]. Its control can was established by revolving, because at high humidity, anaerobiosis may occur in the system [3]. This, can also was controlled by the relationship between effluent injection and the amount of dry mass (DM). The author [5] used an initial rate of 1.47 liters of scum per kg (DM) in the first days up to a rate of 0.21 liters of scum per kg (DM) at the end of the experiment. Other aspects need observed, which are the phases of the composting process, mesophilic and thermophilic phase, both related to the elevation and decrease of temperature and water evaporation.

The state of organic matter decomposition can be measured from the hydrogenic potential (pH) found in the composting system, because for each phase of the process, the pH variation will occur. The initial pH values can be in the order of 4–5 [7], this due to the release of minerals acids and carbonic gas, where at this time the bacteria acidophilus and fungi act in the decomposition of cellulose [3]. Subsequently, the pH can reach values between 7 and 12, due to the formation of organic acids by alkalophiles bacteria [7], when there is stabilization of the compound [3].

With the ease of measuring throughout the process, the temperature profile plays a crucial role in composting. The temperature can range from 10–70°C, mesophilic phase and thermophilic respectively [3]. Its elevation and decrease linked with humidity and microbial activity, as demonstrated in the temperature profile in **Figure 1**.

Another important role of this parameter is the inertization and maturation of the compound over time. Pathogen microorganisms have their inactivation from three days at temperatures higher than 55°C [8], but in composting cells where revolving often occurs; the minimum is 15 days with temperatures above 55°C [4]. Aspects such as raw material, composting system configuration, presence of microorganisms, moisture, oxygen, directly affect temperature. Still the temperature can define the amount of revolving of the composting system. In his work [1], he observed the temperature variation in a process of composting of cattle slaughter residues, and in another study, [4], in a process of composting of pig effluents; both studies presented maximum temperatures did not exceed 55°C. In relation to **Figure 3(a)**, it is also noted that when revolving the composting system, the internal temperature increases significantly. Temperature profiles vary from research to research, [5] observed 72°C in the composting system at 22 days of experiment, [2], observed values not exceeding 52°C, already [9], obtained the maximum temperature of 61°C.

To prepare the composting system it is necessary to note the Carbon/Nitrogen ratio. Both compounds are important in the process, where carbon acts as an energy source and nitrogen as a respirometric source of microorganisms [3], also acting, in cell growth, formation of proteins, amino acids and nucleic acids [2]. The C/N ratio has been observed by several authors [1–4, 6, 9–11], who evaluated that this ratio should not exceed 30/1 in the initial phase, because in high relationships, the degradation of the compounds is delayed, already at the end, when the compound is matured, the ratio may reach 10/1. In this process, much of the carbon is released into the atmosphere in the form of CO2 [6], and nitrogen can be released, when the ratio is low, in the form of ammonia, characterizing bad odor [2].
