*Article* **Waste Management in Dairy Cattle Farms in Aydın Region. Potential of Energy Application**

**Gürel Soyer <sup>1</sup> and Ersel Yilmaz 2,\***


Received: 12 December 2019; Accepted: 18 February 2020; Published: 21 February 2020

**Abstract:** In this paper, the dairy cattle waste management systems on farms in Aydın region in Turkey were investigated. Number of farms and livestock herd size, type of barn, type of machinery and farm labour force were studied. The collection, management and storage systems of manure produced in dairy cattle farms were taken into consideration. Additionally, biogas amount, which is produced from animal waste, was calculated for all districts of Aydın by using the number of livestock animals and various criteria such as the rate of dry matter. Results show that the typical and representative farm in the Aydın region is facility with a total head over 100 heads. 89.6% of the farms have heads in the range of 100 to 200. The amount of biogas that can be produced from all manure collected in Aydın region in the biogas plants is approximately 160,438 m3/day (based on 0.5 m3/day biogas per cattle), which would produce around 100 GWh/year that can be used for own needs of farms owners.

**Keywords:** animal waste; biogas; dairy cattle farms; energy potential; waste management

#### **1. Introduction**

Nowadays, expansion and intensification of large-scale animal feeding operations has resulted in an increase in the size of farms and in the amount of waste produced from farms causing serious problems such as a negative impact on environment and public health in rural areas.

By the end of 2014, according to FAOSTAT [1], 24.99 billion animals were produced on farms all over the World. The livestock sector is one of the fastest growing parts of the agricultural economy. In recent years there has been an increasing demand for cattle production. The large cattle producers are Brazil about 218 million, India 186 million and China 83 million heads [1].

In Turkey, the greatest livestock production belongs to cattle farms, with about 17 million heads of cattle being bred in 2018, resulting in an increase of 33% compared to 2010. Dairy cattle produced about 22 million tonnes of milk and 1 million tonnes of meat in 2018 [2]. Table 1 presents the total amount of animal production from species across years in Turkey.

The breeding and agricultural activities, especially livestock production on an industrial scale, are seen as one of the main sources of natural environment pollution [3,4]. Depending on the farming system, animal farms generate solid (dung) and liquid (liquid manure) animal excrement. In this day and age, no-mulch systems are becoming more and more popular, particularly for livestock production on a large scale. The excrement in this system is so-called liquid manure, i.e., liquid, or a semiliquid mixture of faeces, urine, water and feed leftovers.


**Table 1.** Total amount of animal production in Turkey by species [1].

It is estimated that the cattle residues produced in Turkey reached the value of 1.3 <sup>×</sup> 106 tonnes/year in 2012 [5]. The amount of wet manure from animals could be a major problem for farms. If the wet manure cannot be utilized properly, it can create pollution risk with a potentially disastrous impact on the environment.

Manure management depends on many factors such as the size of the herd and type of manure, as well as available labour, soil type, climate and region [6,7]. Additionally, intensive animal production can be significantly problematic with respect to manure storage and removal [3].

Effluents of unproperly stored manure can flow directly or indirectly into surface waters in open lagoons. As a result, gaseous emissions and odours can also be released upon decomposition of manure, with negative consequences for farmers' fields and livestock farms [8,9]. Fangueiro [10] reported that greenhouse gas (NH3, N2O, CH4) emissions during storing depend on type of manure, i.e., emission from separated solids, are typically higher than from liquid or unseparated manure. Animal manure contains a wide range of micro-organisms which could be a source of hazards to humans and animals. These micro-organisms can cause food contamination and epidemics and are dangerous to public health [3,11]. Therefore, sustainable manure management systems on farms must minimize risks for the environment associated with storage, handling and utilization of manure.

Animal manure contains essential nutrients such as nitrogen, phosphorus, potassium and can be applied to land as a natural fertilizer [7,8], which is the most common method of manure application. Organic matter improves the physical and biological properties of soil, as well as aeration and soil water infiltration [12].

However, in recent years, we have observed a large problem of environmental pollution caused by nitrates connected with irrational use of natural fertilizers in agriculture [13,14]. The manure contains large amount of N in organic form and converted to inorganic form through mineralization process which is ultimately a serious risk to the environment. Manure is applied to the soil at one time (usually by spreading out on the field), so more leaching occurs as compared to chemical fertilizer and the N content may reach the ground and surface waters [15].

Animal manure can also be used as substrate for biogas production in the process anaerobic digestion [16–18]. Biogas is a product of methane fermentation of organic fraction of many types of biomass.

The methane fermentation process consists of four phases (hydrolysis, acidogenesis, acetogenesis and methanogenesis) [19]. The main stages of anaerobic digestion are presented in Figure 1.

**Figure 1.** Stages of anaerobic digestion (methane fermentation process) [20].

The composition of biogas is different and depends on the applied substrates; however, typically it consists mostly of CH4 (40%–70%) and CO2 (15%–60%), as well as other compounds in small amounts: H2O (2%–7%), N2 (2%–5%), O2 (0%–2%) < 1% H2, NH3 (0%–1%) and H2S (0.005%–2%) [8,21].

In the process of biochemical transformations in the absence of oxygen instead of biogas is also produces the nutrient rich organic fertilizer which is easy assimilated by the plants, with a reduction in the odours and the disease-causing agents [19].

The biogas energy potential of Turkey was found to be 2.18 billion m<sup>3</sup> based on the animal numbers in the last agricultural census. The total biogas potential originates from 68% cattle, 5% small ruminants, and 27% poultry. The biogas energy equivalence of Turkey is approximately 49 PJ [5]. After comparing the biogas potential for animal manure of Turkey with that for different countries (Germany 20.6 billion m3, Poland 6.4 billion m3, Italy 1.9 billion m3 and Sweden 7.04 billion m3) [22], Turkey has a high biogas potential, which is associated with the increasing production in the livestock sector.

As of now, only 7% of this potential is used. There are 19 biogas power plants that produce electricity from animal manure in Turkey. The total installed power capacity of the biogas power plants is 43.41 MWe. The range of the installed power capacity is from 0.33 to 6.40 MWe [23].

The collection, storage and utilization of animal manure are the major problems for local livestock farmers. Problems and strategies with respect to manure management should be taken care of on a local scale and adapted to the existing conditions in a given area. There are several studies focused on cattle in Turkey [24–27]. However, region-based studies are few and limited [28,29].

The aim of this study was to investigate the collection and management of manure in the cattle farms in Aydın region. Number of farms, livestock herd size, type of barns, type of machinery for collecting manure, farm labour force and manure management were also studied to evaluate the possibility of using manure as a feedstock for biogas production for energy generation.

#### **2. Materials and Methods**

#### *2.1. Study Area*

Aydın province is located in Aegean Region of western Turkey (Figure 2). The Aegean Region has a typical Mediterranean climate with hot-dry summer and warm-rainy winter. The average annual temperature is 17.6 ◦C, 26.77 ◦C in summer and 9.33 ◦C in winter.

#### *Sustainability* **2020**, *12*, 1614

**Figure 2.** Turkey and Aydın province [30].

The relative humidity of the air is between 48% and 55% and the average rainfall is on the level of 647 mm [31].

The area of Aydın province with 17 districts is 8007 km2. The population was 1,097,746 with density of 140 people/km<sup>2</sup> in 2018. The cultivated area is about 395,494 ha corresponding to 49.3% of soil sources of Aydın and 75,000 ha of cultivated area is used fo cereal production. The main agricultural products in Aydın province are fig, olive, chestnut, cotton and fruits [32].
