One-time animal inventory data can be used for the annual population of static animals like dairy or breading animals [14IPCC 2006a. Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Chapter 10. Emissions from livestock and manure management. ]. Table 1 shows the distribution of populations according to the age and sex for the two understudy animals in the region.

Table 1
Livestock’s population in million.

The average weight of the various breed of a mature male and female cow as well as a mature male and female buffalo is 450 kg, 325 kg, 595 kg and 344 kg, respectively. The average weight of females for cows and buffaloes is aggregated for the milk and non-milk producing animals, and average weight of a young cow and buffalo is 270 kg and 290 kg. On this basis, the weighted average weight of an animal unit (AU) for cow is 319 kg and an AU of buffalo is 353 kg.

For estimating the amount of solid manure excreted from an animal unit, the study has used the IPCC guidelines [14IPCC 2006a. Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Chapter 10. Emissions from livestock and manure management. ] and other literature data as follows:

• − Feeding both cows and buffaloes with green forage supplemented with cellulosic waste (low quality forages) which is one of the most practical and traditional methods [17S.K. Ranjhan, International Livestock Research Institute. Dairy cattle and buffalo. Retrieved on 06.04.2015 from http://www.ilri.org/InfoServ/Webpub/fulldocs/SmHDairy/chap7.html#Feeding.].
• − Digestibility of low quality forages is averagley 50%, i.e. the animal will excrete 50% of the dry matter feed intake that is not digested.
• − The daily dry matter intake for the mature or growing animal is in the order of 2% to 3% of the body weight (average 2.5%). In producing milk cows and buffaloes, the intake is about 4.5% of the body weight [14IPCC 2006a. Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Chapter 10. Emissions from livestock and manure management. ].
• − The ratio of green grass to cellulosic residues on a dry matter basis varies from 1:1 for adult male animals, 3:1 for young animals, and 8:1 for milk producing animals [17S.K. Ranjhan, International Livestock Research Institute. Dairy cattle and buffalo. Retrieved on 06.04.2015 from http://www.ilri.org/InfoServ/Webpub/fulldocs/SmHDairy/chap7.html#Feeding.].
• − An average moisture content of 50% and 10% of the wet weight is considered for green grass and cellulosic residues.

The livestock is divided into four categories _i: adult males, adult females, females in milk, and males or females below three years old (Table 1). Taking into account the above mentioned considerations, the estimation of manure quantity for one Animal Unit (AU) in kg _{(fresh-manure)} day^-1 is given through Eq. 1:

where: LN_i represent the population of livestock category i, BW_i is the body weight of the animal category _i in kg; feed factor_i is the percentage of the weight of the animal category _i (either 2.5% or 4%); non-digestible factor_i of the dry feed is 50%; and the moisture-content_i varies from 30% to 46% depending on the ratios of grass and cellulosic residues for each category as mentioned above. LN is the total population of livestock in Table 1 (19.4 million cows and 22.5 million buffaloes as of year 2014). The livestock household population for each of the categories above is obtained from the Agricultural Census available in Pakistan government website (http://www.pbs.gov.pk/ agriculture-census-publications). The livestock number and the relevant daily manure produced per household are determined for each district.

The focus of the study is on small family size manure-based biogas plants which on average digest the manure of 4 to 10 animal units per day. The design parameters of such biogas plant and biogas yield calculations are presented here. The biogas yield is calculated in m³ biogas for each household based on the kg volatile solid (VS) of the manure input.

Floating drum digesters as the common designed digester for treating diluted dung [18S. Heiske, L. Jurgutis, and K. Zsófia, "Evaluation of novel inoculation strategies for solid state anaerobic digestion of Yam peelings in low-tech digesters", Energies, vol. 8, pp. 1802-1816.
[http://dx.doi.org/10.3390/en8031802] ] are considered. The following characteristics for the cow manure and for the buffalo manure are used:

• − Percentage weight of volatile solids (VS): 17.58 and 18.81 [19Kausar & Muller, 1983. Review on recycling of animal wastes as a source of nutrients for freshwater fish culture within an integrated livestock system. UNDP/FAO Project PAK/80/019. Retrieved on 15.05.2015 from http:// www.fao.org/docrep/ field/ 003/ ac526e/ ac526e02.html. ].
• − General daily biogas production rate: ~0.05 m³ biogas per 1kg fresh dung [20A.S. Munawar, "Renewable energy resource potential in Pakistan", Renew. Sustain. Energy Rev., vol. 13, pp. 2696-2702.
  [http://dx.doi.org/10.1016/j.rser.2009.06.029] ].
• − Percentage total solids of the slurry in the floating drum digester: 7.5%.
• − Density of biogas as 1.28 kg m^-3,.
• − Moisture content of digestate: 93%, with the volatile organic matter of 64% [21S. Kumar, L.C. Malav, M.K. Malav, and S.A. Khan, "Biogas Slurry: Source of Nutrients for Eco-friendly Agriculture", Int. J Ext Res., vol. 2, pp. 42-46.].
• − Biogas losses: 10% [22ADB (Asian Development Bank) Energy access assessment Punjab (Pakistan). ADB energy for all program. Final report 2014: http://www.energyforall.info/wp-content/uploads/2012/07/Punjab-Energy-Access-Assessment-Report-Final.pdf. ].

On the basis of the assumed parameters above, the dilute ratio of manure with water would be around 1.3 kg kg^-1. Equations for calculating biogas yields are presented in Table 2.

Table 2
Equations for calculating biogas yields.

Traditionally, manure is partially used to fertilize the soil. Two sources of GHG emissions from manure are: methane (CH₄) emissions, and direct and indirect nitrous oxide (N₂O) emissions. The common current manure management system in the region is considered as: manure in solid form applied to field regularly, deposition of manure by grazing animal on pasture, and the feces dried in cakes burnt for fuel (Table 3). Since the temperature affects the CH₄ emissions of the manure, the annual average temperature of the districts (10-year mean of minimum and maximum) are collected from the worldweatheronline.com. The average minimum temperature of 11°C to 15°C in few regions in the north and average maximum of 22°C to 33°C in the other regions are observed.

2.3.1. CH₄ Emissions of Manure Management

Following the IPCC calculation method (Tier 1 and Tier 2), for the CH₄ emissions from manure management, first the population of the livestock is subcategorized into animal in milk (cows and buffaloes), and other cattle and buffalo, i.e., subcategory_(t). The percentage distribution of the livestock types in Table 1 is used to estimate the livestock population for each categorized group. In the next step, the specific emission factor EF for each livestock subcategory_(t) is determined through Eq. 7 [14IPCC 2006a. Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Chapter 10. Emissions from livestock and manure management. ].

(7)

where: EF is the annual CH₄ emissions in kg CH₄ FU^-1; VS_t is the relative volatile solid of manure for livestock subcategory_(t) in kg_(dry-matter) FU^-1; B_o is the maximum CH₄ emissions from livestock subcategory _(t) in m³ kg_(VS)^-1; MCF_st is the methane conversion factor in temperate, warm and cold climate for each manure management system_(s) of the subcategory_(t) in percentage (three dominant manure management systems are pasture, daily spread, and fuel cake); MS_st is the fraction of the manure management system_(s) for the livestock subcategory_(t). A density of 0.67 kg m^-3 is used to convert the CH₄ volume to mass. The base data for components of Eq. 7 is given in Table 3. The volatile solids (VS) of manure for cows and buffalos are adopted from [19Kausar & Muller, 1983. Review on recycling of animal wastes as a source of nutrients for freshwater fish culture within an integrated livestock system. UNDP/FAO Project PAK/80/019. Retrieved on 15.05.2015 from http:// www.fao.org/docrep/ field/ 003/ ac526e/ ac526e02.html. ] as 14% and 16% of the fresh manure weight, with moisture content of 82% and 81%, for cows and buffaloes, respectively.

Table 3
Base data used for CH₄ emissions of manure management in the region [14IPCC 2006a. Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Chapter 10. Emissions from livestock and manure management. ].

2.3.2. N₂O Emissions of Manure Management

According to the IPCC [14IPCC 2006a. Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Chapter 10. Emissions from livestock and manure management. ], the default emission factor for direct N₂O emissions from daily spreading of manure is assumed to be zero. However, the related indirect N₂O emissions as well as the direct and indirect N₂O emissions associated with the manure management in pasture is calculated from IPCC methods on managed soil [15 IPCC, 2006b. Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Chapter 11:N₂O Emissions from Managed Soils, and CO₂ Emissions from Lime and Urea Application.]. The direct and indirect N₂O emissions refer to the emissions from manure-N inputs to manage soil, and to the ammonium-N and NOx emissions plus leaching NH⁴⁺ and NO^3-, respectively [15 IPCC, 2006b. Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Chapter 11:N₂O Emissions from Managed Soils, and CO₂ Emissions from Lime and Urea Application.].

The average total-N content of cow’s and buffalo’s manure is considered as ~1.0% on dry basis [23M.K. Hasanuzzaman, U. Ahmed, K. Nahar, and N. Akhter, "Plant growth pattern, tiller dynamics and dry matter accumulation of wetland rice (Oryza sativa L.) as influenced by application of different manures", Nat. Sci., vol. 8, no. 4, pp. 1-10.http://www.e3journals.org/ cms/ articles/ 1411271518_Sohail%20et%20al.pdf-25A. Yadav, R. Gupta, and V.K. Garg, "Organic manure production from cow dung and biogas plant slurry by vermicomposting under field conditions", Int. J. Recycl. Org. Waste Agric., vol. 2, pp. 21-28.
[http://dx.doi.org/10.1186/2251-7715-2-21] ]. The total N₂O emissions comprise of the summation of direct emissions (Eq. 8) and indirect emissions (Eq. 9) formulated as follows [15 IPCC, 2006b. Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Chapter 11:N₂O Emissions from Managed Soils, and CO₂ Emissions from Lime and Urea Application.]:

(8)

where: N₂O-direct is the direct-N₂O emissions into atmosphere as kg N₂O FU^-1, FPR_t is the annual amount of organic N deposited on pasture from grazing livestock subcategory_(t) in kg N FU^-1, EF₁ is the emission factor for N₂O emissions of FPR that is 0.02, Constant 44/28 is the conversion factor of N₂O-N to N₂O emission. MS is the manure management systems (in percentage) for each livestock subcategory _(t) cited in Table 3.

(9)

where: N₂O-indirect is the annual amount of N₂O emissions produced from atmospheric deposition of N volatilized from managed soils in kg N₂O FU^-1, Frac₁ is the fraction of FAM and FPR which will be volatilized as NH₃ and NOx that is 0.20, EF₂ is the emissions factor for N₂O emissions ((kg N₂O-N per kg NH₃-N+NOx-N volatilized) that is 0.01, Frac₂ is the fraction of leaching and runoff of FAM and FPR that is 0.30, and EF₃ is the emissions factor for N₂O emissions from N leaching and runoff that is 0.0075.

One of the important resources for improving soil conditions is the supplement organic matters in the animal wastes [25A. Yadav, R. Gupta, and V.K. Garg, "Organic manure production from cow dung and biogas plant slurry by vermicomposting under field conditions", Int. J. Recycl. Org. Waste Agric., vol. 2, pp. 21-28.
[http://dx.doi.org/10.1186/2251-7715-2-21] ]. As mentioned earlier, in the region ~ 52% of the collected manure is used for fuel, and the rest is mainly managed either as daily spreading or as pasture Table 3. In the alternative manure management for biogas generation, the digestate can be used as the organic supplement for the soil. However, the GHG emissions associated with digestate should also be taken into account.

For this purpose, the emission factors for N₂O emissions (kg N₂O-N per kg N in slurry) are 0.01 for direct emission; 0.002 for indirect volatilized; and 0.0023 for indirect runoff [15 IPCC, 2006b. Guidelines for National Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other Land Use. Chapter 11:N₂O Emissions from Managed Soils, and CO₂ Emissions from Lime and Urea Application.]. The average total N of dung digestate is 1.0% [26P. Wallace, 2011. Digestates: Realizing the fertilizer benefits for crops and grassland. Project code: OAV036-210. Retrieved on 01.01.2015 from http://www.wrapcymru.org.uk/sites/files/wrap/Farmer%20guidance%20final%20-%20Cymru.pdf.] on dry weight basis. The average percentage phosphorous (P) and potassium (K) are about 1.1% [21S. Kumar, L.C. Malav, M.K. Malav, and S.A. Khan, "Biogas Slurry: Source of Nutrients for Eco-friendly Agriculture", Int. J Ext Res., vol. 2, pp. 42-46., 27M. Yasin, and M. Wasim, "Aanaerobic digestion of buffalo dung, sheep waste and poultry litter for biogas production", J. Agric. Res. (Lahore), vol. 49, pp. 1-10.http://www.jar.com.pk/upload/1374663342_88_35__73Paper-9-JAR-49%281%29-2.pdf]. The percentage content of P and K for the dry manure is ~0.7% [23M.K. Hasanuzzaman, U. Ahmed, K. Nahar, and N. Akhter, "Plant growth pattern, tiller dynamics and dry matter accumulation of wetland rice (Oryza sativa L.) as influenced by application of different manures", Nat. Sci., vol. 8, no. 4, pp. 1-10.http://www.e3journals.org/ cms/ articles/ 1411271518_Sohail%20et%20al.pdf, 28S Akhtar, S Shakeel, A Mehmood, A Hamid, and S. Saif, Comparative analysis of animal manure for Soil conditioning. Int. J. Agron. Plant Prod. 2013; 4 (12): 3360-3365.] with an assumed 93% of moisture content for the digestate [21S. Kumar, L.C. Malav, M.K. Malav, and S.A. Khan, "Biogas Slurry: Source of Nutrients for Eco-friendly Agriculture", Int. J Ext Res., vol. 2, pp. 42-46.].

The biogas generated in the managed manure system can benefit the households in several ways. This study has focused on the first dominant benefit which is cooking; therefore, it is required to take into account the realistic reference systems that would otherwise be replaced.

In rural areas, more than 93% of the households use traditional fuels for cooking, mainly wood fuel (~53%), manure cake (~18%), and crop residues (~21%) [29U.K. Mirza, N. Ahmad, and T. Majeed, "An overview of biomass energy utilization in Pakistan", Renew. Sustain. Energy Rev., vol. 12, pp. 1988-1996.
[http://dx.doi.org/10.1016/j.rser.2007.04.001] , 4P. Bojesson, and M. Maria Berglund, "Environmental systems analysis of biogas systems - Part II: The environmental impact of replacing various reference systems", Biomass Bioenergy, vol. 31, pp. 326-344.
[http://dx.doi.org/10.1016/j.biombioe.2007.01.004] , 30WHO (World Health Organization), 2005. Situation Analysis of Household Energy Use and Indoor Air Pollution in Pakistan. WHO/FCH/CAH/05.06. Retrieved on 20.05.2015 from http://whqlibdoc.who.int/hq/2005/WHO_FCH_CAH_05.06.pdf.]. Biogas will substitute these biogenic sources, and therefore, for achieving a right GHG emission balance, the emissions of CO₂, CH₄ and N₂O of these fuels and those of biogas is estimated through the IPCC emissions factors [16 IPCC, 2006C. IPCC Guidelines for National Greenhouse Gas Inventories. Volume 2: Energy.] and the stationary combustion biomass under related IPCC categories [31 NIR, 2014: Memo item on CO₂ emissions from biomass including 1A1, 1A2, 1A4: CH₄ and N₂O emissions from the stationary combustion of biomass.]. The emissions of reference flows are estimated in Table 4.

Table 4
Data for calculating the biogas equivalent for various reference flows ^a

Around 0.2 to 0.4 m³ biogas per capita per day is sufficient for cooking in Pakistan [20A.S. Munawar, "Renewable energy resource potential in Pakistan", Renew. Sustain. Energy Rev., vol. 13, pp. 2696-2702.
[http://dx.doi.org/10.1016/j.rser.2009.06.029] ]. The factor varies with the household size. From the neighboring country’s experience like India, with an average rural household size of 5.5, about 0.23 m³ capita^-1 day^-1 of biogas can satisfy the cooking demand of the rural communities [32IARC (International Agency for Research on Cancer). World Health Organization. Household Use of Solid Fuels and High-temperature Frying 2010; 95. Retrieved on 24,05,2015 from http://monographs.iarc.fr/ENG/Monographs/vol95/mono95.pdf.]. For the average household size of Punjab’s rural areas as 6.5 [33A.W. Bhutto, A.W.A. Bazmi, and G. Zahedib, "Greener energy: Issues and challenges for Pakistan: Biomass energy prospective", Renew. Sustain. Energy Rev., vol. 15, pp. 3207-3219.
[http://dx.doi.org/10.1016/j.rser.2011.04.015] ], the study has assumed 0.27 m³ capita^-1 day^-1 of biogas for cooking. On the considerations above, each rural household in Punjab will need averagely 3.5 kg of wood, 1.6 kg of dung and 2.4 kg of crop residues to fulfill the daily energy demand for cooking. The substituted biomass fuels and their avoided GHG emissions are accordingly calculated.

The biogas digestate produces organic nutrients as the by-product which are considered as environmental friendly biofertilizers necessary for the plant growth [21S. Kumar, L.C. Malav, M.K. Malav, and S.A. Khan, "Biogas Slurry: Source of Nutrients for Eco-friendly Agriculture", Int. J Ext Res., vol. 2, pp. 42-46.]. The nutrient trade-offs of the two management systems are comparatively shown in Fig. (2). The result shows that averagely, each kg fresh cow’s manure (and buffalo’s manure) fed into the digester produces ~0.12 (and 0.14 kg) dry digestate. Taking into account the percentage content of the total nitrogen, phosphorous, and potassium of the manure and of the digestate in section 2.4, and considering 20% loss of digestate slurry, the relative level of these three organic nutrients for the two manure management systems with and without biogas generation is shown in Fig. (1).

Fig. (2) Comparing NPK nutrient credits in manure management with and without biogas production.

The alternative biogas generation takes advantage of digesting the quantity of the manure which would otherwise be burnt for fuel in the traditional management. It is estimated that, in overall, there would be 51%-63% of additional N, 154%-176% of additional P, and 142%-162% of additional K (depending on the type of AU-cow or AU-buffalo) for the rural community. For the case study of Punjab where each household (HH) averagely holds 6.1 AU of cows and 5.5 AU of buffaloes, there would be annual extra amounts of about ~182 kt NPK available for the whole Punjab’s households if biogas management is practiced. Most of the soils in Pakistan are poor in nutrient availability for optimal crop productivity, and the calcareous nature of soils has caused a low phosphorous P fertility [34H Nazli, SH Haider, S Hausladen, A Tariq, H Shafiq, S Shahzad, A Mehmood, A Shahzad, and E Whitney, Pakistan Rural Household Panel Survey 2012 (Round 1): Household Characteristics.]. The considerable higher NPK potential from biogas digestion would likely contribute to overcome the nutrient deficiency especially for phosphorous.

The likely further indirect GHG reductions from the excess nutrient produced from digester is expected. For instance, the mean yield of maize grain has increased when the plant is treated with biogas slurry as compared to the treatment with farmyard manure [35M. Ashraf, F.A. Tahir, M. Nasir, M. Bilal-Khan, and F. Umer, "Distribution and indexation of plant available nutrients of district layyah, Punjab Pakistan", Am. J. Agri., vol. 3, no. 2, pp. 16-20.
[http://dx.doi.org/10.11648/j.ajaf.20150302.11] ]. The application of stabilized digestate is assumed to be less harmful and more environmental benign [36A. Nasir, M. Mahmood Riaz, and M.A. Khan, "Comparative study of biogas slurry with farmyard manure as fertilizer on maize crop," Sci.Int (Lahore),22(4),297-301. , 37CT Lukehurst, P Frost, and T Al-Seadi, IEA Bioenergy- Task 37: Utilisation of digestate from biogas plants as biofertiliser 2010. Memo item on CO2 emissions from biomass.] while the farmyard manure may contaminate the environment with a relatively higher content of heavy metals if not managed properly [38H. Insam, M. Gómez-Brandón, and J. Ascher, "Manure-based biogas fermentation residues - Friend or foe of soil fertility?", Soil Biol. Biochem., vol. 84, pp. 1-14.
[http://dx.doi.org/10.1016/j.soilbio.2015.02.006] ]. Nevertheless, there is a lack of certainty in selecting the appropriate reference systems and in determining losses from crop uptake to identify these indirect impacts.

The result of the life cycle GHG flows associated with the manure management with and without biogas generation is presented in Table 6.

Table 6
Average life-cycle GHG profiles for manure management systems.

The advantage of around 50% overall GHG reductions for alternative management system in Table 6 is due to the avoided traditional cooking fuel (wood, crop-residues and dung) which accounts for ~76% of the GHG emissions associated with the traditional management. The total life-cycle GHG reduction of the alternative manure management for biogas generation in the region could reduce around 18.7 million-t CO₂ eq yr^-1 (more than 7% of the total GHG emissions of the country). The savings of 17.7 (and 17.6) kg wood, and 11.9 (and 11.5) kg crop-residues per functional unit would potentially conserve 7.8 million-t wood and 5.2 million-t crop-residues per year. Moreover, there would be external societal benefits specially to women and children due to using a cleaner cooking fuel and saving the time and effort of gathering wood [1International Energy Agency. Energy access outlook from poverty to prosperity. World energy outlook special report 2017].

Another benefit of the alternative manure management is the electrification. The electricity access in rural Punjab is almost 80% which is rather high compared to other provinces in Pakistan; however, there are 621 un-electrified villages in the province [26P. Wallace, 2011. Digestates: Realizing the fertilizer benefits for crops and grassland. Project code: OAV036-210. Retrieved on 01.01.2015 from http://www.wrapcymru.org.uk/sites/files/wrap/Farmer%20guidance%20final%20-%20Cymru.pdf.]. The outrages in some rural areas causes the electricity cut even up to 12 to 20 hours per day. The estimated saved wood-fuel and crop residues can potentially be used for electricity generation, thus reducing the electricity supply shortage for the rural regions. Considering the LHV of wood and crop residues in Table 4, and assuming an electricity efficiency of 25% and 7000 operation hours of the plant, the total annual power generation from the saved local biomass sources for each district can be estimated. The potential electricity capacity could be of minimum 8 MW in Islamabad up to maximum 119 MW in Jhang, with a total potential of 1.9 GW electricity for the whole rural communities. Taking into account that Pakistan is highly dependent on fossil fuel for electricity production, further indirect GHG reductions is expected. However, the true credit depends on the logistic conditions and the local markets which deserve to be investigated in a future study.

The biogas loss (leakage) not only reduces the energy efficiency [4P. Bojesson, and M. Maria Berglund, "Environmental systems analysis of biogas systems - Part II: The environmental impact of replacing various reference systems", Biomass Bioenergy, vol. 31, pp. 326-344.
[http://dx.doi.org/10.1016/j.biombioe.2007.01.004] ], but also contributes significantly to the GHG emissions. Results in Table 6 indicate that, averagely, a ten percent biogas leakage accounts for almost 23% of the total life-cycle GHG emissions from biogas digestion. It also reduces the local biomass sources by ~10% (not shown in the table). A high biogas leakage of 40% from family biogas plants in rural developing countries is not very unlikely [12S Bruun, SL Jensen, VTK Vu, and S. Sommer, Small-scale household biogas digesters: An option for global warming mitigation or a potential climate bomb? 2014. Renewable and Sustainable Energy Reviews; 33: 736–741.
[http://dx.doi.org/10.1016/j.rser.2014.02.033] ]. In the study, a biogas loss of greater than 38% could result in an overall GHG emission rather than a GHG reduction. Notably, the biogas leakage is a critical bottleneck in achieving sustainability in the alternative manure option.

While efforts have been made to investigate the economic valuation of manure-to-biogas in rural developing communities [22ADB (Asian Development Bank) Energy access assessment Punjab (Pakistan). ADB energy for all program. Final report 2014: http://www.energyforall.info/wp-content/uploads/2012/07/Punjab-Energy-Access-Assessment-Report-Final.pdf. , 40GIZ (Deutsche Gesellschaft für Internationale Zusammenarbeit). Techno-economic feasibility study for biogas system application using cattle farm waste Punjab province–Pakistan 2013. Retrieved on 20.05.2015 from http:// energy.punjab.gov.pk/ downloads/Revised%20Techno - economic%20Feasibility%20Study_ Punjab_08%2002%202013%20.pdf.], this study has identified certain favorable conditions and limitation of manure-to-soil and manure-to-biogas.