*2.2. Methods*

The aim of this study was to investigate manure collection and management in cattle farms in the Aydın region of Turkey and determine the energy potential of the waste generated on farms.

In this study, a survey was conducted by interviewing the owners of 87 farms located in 17 districts of Aydın province and each farm was photographically documented.

The survey included general topics presented below:


In addition, the energy parameters of manure waste as a potential substrate for the biogas production were also examined. The tests were carried out in accordance with the following standards:


Based on the data obtained from 87 farms livestock size in the study region, potential of biogas and electricity production were calculated using equation 1 and 2 below:

Biogas production (BP) [33]:

$$\text{BP} = \text{N}\_{\text{c}} \times \text{C}\_{\text{s}} \tag{1}$$

where: Nc—the number of cattle, C—production of manure per day/cattle (on the basis of an assumption of 0.4 m3/day/cattle [34].

Electricity production (EP) [21]:

$$\text{LEP} = \text{BP} \times \text{LHVx@CH}\_4.\tag{2}$$

where: %CH4—methane content in the biogas (on the basis of an assumption it is 62%), LHVCH4—low heating value of methane (21 MJ/m3)—1.7 kWh in cogeneration process: 1.7 kWh electricity and 2 kWh heat) [34].

#### **3. Results and Discussion**

In Aydın province, many of farms are located in the districts: Efeler (18 farms), Cine and Kuyucak (12 farms) and Söke (10 farms). Table 2 presents number of cattle in districtes of Aydın.


**Table 2.** Total amount of cattle in Aydın's districts [35].

Farms in Aydın province usually have more than 100 cattle and the number of animals in the 89.6% of the farms range between 100 and 200 heads.

The study shows that 69.55% of the farmers are under age 50. The ages of the youngest and oldest farmers are 28 and 74, respectively. The percentage of owners who have a university degree was 14.9%, whereas most of the owners have an elementary school degree (43.7%). Only farmers with higher education showed an interest in application of new technologies.

Manure storage type is of importance in terms of impacts on gaseous emissions and the flexibility it offers for land application and hence the potential for nutrient losses to ground and surface waters.

Generally, owners of farms have noticed the problem of disposal of manure, the facility must minimize the impact on water quality, especially on groundwater and surface water. It is indicated that the manure storage facility should be located at least 100 m away from the water resources [36].

In the Aydın region, the distance between open-air manure storage and water resources, as well as source of drinking water supplies, is 96 m on average. Çayır and Atılgan [37] examined about 74 farms in Burdur province and determined the distances to be 1–10 m in 39 farms, 11–20 m in 20 farms and 21–30 m in 10 farms, and 31 m or more in 5 of 74 farms. According to Mutlu [38], Jacopson et al. [39] and Nizam et al. [40], this distance should be much longer.

In the study area, manure storage facilities are located in the open area. The most common type of manure storage is midden (60%), and 30% and 10.3% of farms store the manure on flat ground and on leak-proof pits, respectively. Figure 3 presents the types of manure storage used in Aydın region. Manure stored on flat ground is shown in Figure 4.

**Figure 3.** Types of storage used in Aydın region.

**Figure 4.** Manure storage on flat ground.

Study shows that 66.6% of farms do not have manure storage pits on protected ground (concrete floor). Therefore, there is a danger of contamination of ground water with nitrogen compounds.

For example, according to the survey by Smith et al. [6], manure is stored in concrete floor compounds (40%) and temporary field heaps (60%) in England. Loyon [41] stated that 23% of facilities for storing manure are covered in France.

Manure is usually stored for many months, and during its decomposition, manure emits unpleasant gases such as ammonia and hydrogen sulphide and impacts the health and comfort of surrounding people. Another problem is to minimize odour from manure storage locations as well as from open barns, which depends on the size of the intensive livestock operation, the type of livestock or manure management system and storage time.

The results of this study show that 48.2% of farms have closed-wall barns, 41.4% semi-open barns and rest of them have open sheltered barns. Semi-open barns are shown in Figure 5.

The conventional method of handling manure has been to use sufficient bedding to keep the manure relatively dry and then to move it out of the confinement area and deposit it into a manure pile [42].

In large production units, manure is handled both mechanically and hydraulically. Mechanical removal of the wastes is normally done with tractors, manure spreaders or scrapers with permanently installed equipment, such as shuttle conveyors, floor augers or pumps.

The information collected from the dairy farms assessed in this study showed that 67.8% of the farms used tractor shovels for the collection of manure produced in barns. The percentage of manual collection was 14.9%, and there were only 9 farms (10.4% of the farms evaluated) in which the manure was collected with scrapers equipped with chain. 89.7% of the farms do not have any impermeable manure pits.

**Figure 5.** Semi-open barns.

The most common waste management strategy on farms is to apply the manure to the land. Atılgan et al. [43] divided it according to content of solids, i.e., above 25% solid fertilizer; 10–20% semi-solid and 0–10% content of soils is called liquid manure. All produced manure in the studied farms is used in agriculture as fertilizer, mostly for their own purposes, and only 12.6% of farms sell it. The studied farms utilize only the solid manure, which provides minimum benefit because of the loss of organic nitrogen content during long storage, while it can also cause serious environmental pollution.

It is stated that the main source of nitrate contamination in groundwater is agricultural fertilizers.

In the Aydın region the high level of nitrite (0–124 mg/L) [44] in groundwater used for the irrigation was noted. The average level of nitrite in the surface water is in the range of 0.01–0.7 mg/L, nitrate 1.20–3.70 mg/L, ammonia 004–5.20 mg/L [45]. According to the World Health Organization (WHO) [46], the standard nitrate level in drinking water is 50 mg/L. Groundwater is used as irrigation (from 8–32 m deep) and drinking (>32 m deep). Elevated nitrate concentrations in groundwater can cause public health problems. Now Turkey has updated regulations aiming to combat agricultural nitrate pollution in rivers and soil. The revised rules include procedures and principles for determining, reducing and eliminating nitrate pollution [47].

Due to the increase in the Turkish population, and therefore the increase in demand from the animal sector, contamination from pollutants may also cumulatively increase in the next years. Regulations are required in order to control manure management, especially the localization of manure storage and type of floor construction for its temporary storage, as well as the limits for the use of manure as fertilizer.

Baytekin [33] claims that, under normal conditions, a healthy cow produces 40–45 kg of manure per day. According to this value, the total manure amount obtained from the research area is as presented in Table 3.



\* calculated from obtained data.

The production of biogas from manure, in particular, is one of the alternative utilization methods of organic wastes that can be implemented in this region. This study also attempts to identify the biogas potential of the Aydın region basing on obtained data of animal manure production.

As a first step for this application, the energy parameters of manure, as a potential feedstock for the biogas production were tested. Obtained energy parameters of manure is presented in Table 4.


**Table 4.** Energy properties of manure.

wt—weight percentage; dm—dry mass; HHV—High Heating Value; \*—calculated on the basis of the obtained difference.

One of the key parameters in terms of the efficiency of biogas production is associated with the high content of organic matter in wastes, and this determines the course of the fermentation process and the volume of the biogas [21]. The tested samples have a high content of organic matter (74.62%), which is comparable with data obtained by Zue et al. [48], it may range from 68% to 76%. For methane fermentation, especially for the growth of microorganisms, one of the important factors is the ratio of C:N (optimum 20–30:1) [49]. The ratio of C:N in the waste (24:1) is adequate in this respect.

For the Aydın province, based on the amount of produced waste, it is possible to obtain about 160,438 m<sup>3</sup> biogas/day, assuming 0.5 m3/day biogas per cattle. Table 5 contains total amount of produced biogas in Aydın and LPG equivalent.

**Table 5.** Total amount of produced waste and biogas in Aydın and its LPG equivalent.


\* calculated from obtained data.

It gives production of electricity on level 99,552 MWh annually. In Aydın in 2012 electricity consumption was 1,860,667 MWh. In the case of the use of biogas, which can be substituted for conventional fuels, 5.4% of electricity can be covered by biogas.

There is only one biogas power plant—Efeler BGEPP—in the Aydin region, with a max installed power of 4.8 MWe. Because of the distributed allocation of small-capacity livestock farms in the region, and also due to the low interest of farmers in installing their own small biogas installations, it is proposed to build centralized facilities.

Considering the use of only half of the manure generated in the region, it is possible to install 7 biogas power plants with a capacity 4.8 MWe in different locations. Because of the topography and the distances between farm locations, the Aydın region can be divided into four districts, in which 3-4 biogas power plants can be installed with capacities similar to the Efeler BGEPP facility.

There are some funds that support investments in renewable energy sources in Turkey such as: *Renewable Energy Resources Support Mechanism (YEKDEM)*, coordinated by the Energy and Natural Resources Ministry, the regional scale *Agriculture and Rural Development Support Institution (TKDK)*, supported by the Agriculture and Forestry Ministry, and also local development agencies subordinate to teh Ministry of Development, for example, the South Aegean Development Agency (GEKA) serving, i.a., the Aydın region.

According to the Turkish National Energy and Mining Strategy, it is a top priority for Turkey to generate 30% of its electricity from local and renewable resources by 2023. The costs of achieving this target by 2023 are estimated to require investment in renewable energy generation of around 21 billion USD (1,5 billion USD/year) [50]. In the case of Turkey, which is a net energy importer, 73% of its energy needs come from foreign suppliers, and investments in a local and secure energy supply is main pillar of the energy sector.

Biogas, biomass, and geothermal energy resources are expected to comprise a considerable part of RES with the rapid growth in utilization of these resources in the market [51].

Biogas can be used for heating and electricity production, providing local autonomy for the region in the face of the increasing cost of fossil fuels.

Manure storage facilities on farms should be considered to be a temporary solution, and farmers should have knowledge about the negative influence on the environment caused by improper treatment of manure. Education and financial support in changing the approach to animal waste management can be a key factor.

The conversion of animal waste to biogas through anaerobic digestion processes can provide added value to manure as an energy resource and reduce the environmental problems associated with animal waste. It is worth mentioning that dairy cattle manure is endowed with considerable biogas production, offering numerous benefits with respect to environmental, agricultural and socio-economic standards.

**Author Contributions:** Conceptualization, E.Y.; methodology, E.Y. formal analysis, E.Y.; investigation, G.S.; resources, G.S.; writing—original draft preparation, G.S.; writing—review and editing, E.Y.; supervision, E.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was funded by Scientific Research Fund of Adnan Menderes University (Project No: ZRF12049).

**Conflicts of Interest:** The authors declare no conflict of interest.
