6.2.1. Nutritional strategies for reducing the environmental impact of animal agriculture

Feeding strategies can also be used to reduce livestock manure yield and potential emissions from manure management. Ref. [24] reported that chickens fed low protein diets had lower manure output and reduced nitrogen output intensity compared to those on higher protein regimes. The studies also found that amino acid supplementation, enzyme supplementation and manure treatments with various types of alum resulted in additional reduction in nitrogen excretion in chickens [24–27]. The implication of the finding is that lower manure and nutrient output reduces their potential environmental impacts.

#### 6.2.2. Manure treatment

Manure treatment can be physical, biological or chemical. The objectives of manure treatment include reduction of manure volume, improvement of its applicability and/or increase in fertilizer value. Forms of treatment include dehydration, solid separation, anaerobic and aerobic lagoons, nutrient fortification, pelletizing, composting, refining and methane digester [22, 28].

6.3. Strategies for odor control from livestock manure

gases and reducing their release into the atmosphere.

and should not be in an area that allows nutrient run-off.

prone to release odor into the atmosphere.

feasible.

manure reduces odor [39].

7. Future of manure management

Manure is one of the most common and main sources of odor in a livestock operation. Ref. [28]

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• Plan, design, construct and manage livestock operations in a way that minimizes the impact of odor on neighbors. This will require reducing the formation of odor-forming

• The location of livestock operations, particularly outside lot systems, should maintain a safe distance from residents and other odor-sensitive land use. This is because odors may be generated from these systems even with good facilities design and management practices.

• As much as possible, manure storage facilities should not be located close to residential areas. • Solid manure from farm animals can be stacked on a temporary basis outside the livestock building. Farmstead stockpiled manure should be on a hard surface, preventing direct contact with the soil. Where they are in direct contact with the soil, they should be temporary and removed from time to time. Such grounds should be left vegetated for at least 3 years to allow enough time for the nutrients to be taken up by plants. Stockpiles could also be covered with straw, wood chips and other materials and/or treated with additives such as lime to help reduce odors and pests. Field stockpiles must be temporary

• Manure storage facilities are temporary measures to hold manure-pending soil application. Therefore, where it is economically and technically feasible, covered manure storage facility should be used. This is because uncovered manure storage facilities are more

• Manure should be incorporated into the soil almost immediately after application where

• Odor from manure can also be reduced through treatment. For example, composting

Manure management is an integral part of the waste management system. Therefore, current trends shaping waste management policies and practices will dictate the direction of future shifts in manure management. Several authors have identified some trends and those expected to influence future animal manure management systems, policies and practices. In a bid to reduce the quantity of wastes generated in the production, multiple industries are now leaning towards sustainable innovations and processes in the sourcing and production of items; the use of renewable resources and environmentally friendly raw materials is being favored, and products and materials that cannot be recycled are being eliminated from the production.

provided the following guidance on strategies for odor control from livestock manure:

Treatment with alum: Alum (aluminum sulphate), sodium bisulphate and mineral or organic acids are some of the materials that could be used for litter or manure amendments for N and NH3 as well as other benefits [29]. Amendments of manure could be utilized to further control mineral volatilization and other forms of releases from animal manure. Alum, also referred to as filter alum (Al2(SO4)2), is used as a flocculating agent in the purification of drinking water and waste-water treatment. Use of alum is an effective method of reducing nitrogen loss due to ammonia volatilization [30]. Use of alum in chicken manure amendment would lead to decreases in animal-house ammonia level, reduction in energy usage, improvement in animal performance, precipitation of soluble phosphorus, reduction of phosphorus and heavy-metals run-off and imposition of drying effect that reduces litter moisture. Manure treated with 1.5% alum inclusion had higher nitrogen content than untreated manure during a week of storage [27]. Nitrogen concentration in alum-treated manure tends to be elevated compared to normal manure. Elevated fecal nitrogen in stored alum-treated manure was attributed to a lower magnitude of nitrogen loss in treated compared with untreated manure and enhances its fertilizer value.

Composting: This is a natural process of aerobic decomposition or fermentation of manure by micro-organisms. Compost is rich in organic matter and has the ability to improve soil health. Compost can be made either through heap/pile or through pit method. Some of the benefits of compost in the soil include improved fertility, water-holding capacity, bulk density and biological properties [31]. A lower number of viable weed seeds in composted manure contributes to the reduction in the use of herbicides or tillage requirements for weed control [32]. Composting could be effective in killing some pathogens in manure. It also leads to up to 50–60% of reduction in the volume and density of manure thereby making its transportation more energy efficient than that of non-composted manure [33].

Anaerobic digestion: Anaerobic digestion of manure is the processing of manure to produce energy, mainly biogas. Anaerobic digestion of manure can be made more efficient through the use of co-products such as water hyacinth, corn silage and so on. Methane yield differs from various animal manure types. Rice straw (550–620 m3 biogas/tonne DM), maize straw (400– 1000 m3 biogas/tonne DM), vegetable wastes (400 m3 biogas/tonne DM) and kitchen wastes (400–1000 m3 biogas/tonne DM) yield relatively more biogas than animal manure with biogas yield of 200–300, 250–500, 310 and 300–400 m3 biogas/tonne DM for cattle, pig, poultry and sheep manure, respectively [34]. Biogas from manure digester can be used for cooking instead of the direct burning of biomass. It can also be used to power the generator for electricity. The composition of biogas produced for bio-digester is 50–70% methane, 30–45% carbon dioxide, 0– 3% nitrogen, 0–3% oxygen, 0–3% hydrogen [22] and the heating value of the gas ranges from 18 to 25 MJ/m3 [35, 36]. Whereas the biogas market may currently be underdeveloped in several countries of the world, it holds great potentials if rightly channeled to meet some of the national energy targets. The digestate from manure digestion is valuable as a fertilizer and should be used as such. However, this may require additional technologies and costs because of the high moisture content [37]. Sales of bio-energy and compost/manure substrate from biogestion can be economically viable while at the same time contribute to a safe and sane environment [38].
