Sewage sludge and the energy balance of Jerusalem artichoke production - a case study in north-eastern Poland

Krzysztof Józef Jankowski, Bogdan Dubis, Marcin Kozak
2021 Energy  
Sewage sludge is a specific by-product of wastewater treatment and its use as fertilizer is the most rational and the cheapest strategy for managing this waste product. In this study, the production of aerial biomass, energy inputs and the energy efficiency ratio of Jerusalem artichoke (JA) fertilized with sewage sludge at rates equivalent to 100 and 160 kg N ha −1 were evaluated in a field experiment conducted in north-eastern Poland in 2018-2020. In conventional treatments supplied with
more » ... l fertilizer, energy inputs were determined at 23.5-28.1 GJ ha −1 in the year of plantation establishment and at 12.6-18.3 GJ ha −1 in the second and third year. In treatments fertilized with sewage sludge, the demand for energy was lower by 27-32% in the first year and by 48-54% in the second and third year. Regardless of fertilizer type the optimal nitrogen rate was 100 kg ha −1 (11.7-11.9 Mg ha −1 DM y −1 ). The biomass of JA plants supplied with 100 kg N ha −1 was also characterized by the highest energy output and energy gain. Energy gain was 5-11% higher per hectare, and the energy efficiency ratio was nearly twice higher in treatments supplied with sewage sludge than with mineral fertilizer. Keywords: Helianthus tuberosus L., energy inputs, energy output, energy gain, energy efficiency ratio J o u r n a l P r e -p r o o f These requirements are met by Jerusalem artichoke (JA) (Helianthus tuberosus L.) [11, 12] . Jerusalem artichoke is native to North America, and it became naturalized in regions with a temperate climate [6, 12, 13] , within a latitudinal range of 40°N to 55°N [6]. In Europe, JA probably spread from the south to other parts of the continent, from France, through Germany, Poland, the Ukraine, Belarus and Moldova, to Russia and the Russian Caucasus [14] . Jerusalem artichoke can also be produced commercially in regions with a colder climate, including in the Nordic countries [14, 16] . Jerusalem artichoke is grown as a perennial crop for the production of aerial biomass and as an annual crop for the production of tubers and aerial plant parts [6, 15, [17] [18] [19] . The species is characterized by a rapid growth of aboveground plant parts, and it can be harvested several times during the growing season, mainly in regions with a continental climate [20] . In the cold temperate climate (Central and Eastern Europe), biomass is harvested once (or, less frequently, twice) during the growing season because JA tubers are dormant in the winter months (December to March) [21] [22] [23] . Tubers can be left in soil even in colder climates because they are abundant in inulin that offers protection against low temperatures [24]. Planted tubers tolerate temperatures as low as -30°C [25] or even -50°C [26]. Jerusalem artichoke is characterized by rapid biomass growth, and it has low soil, water and agronomic requirements [6,20,27-29]. The potential productivity of JA tubers and lignocellulosic biomass is estimated at 70-100 Mg ha −1 y −1 of fresh matter (FM) [18,30,31] and J o u r n a l P r e -p r o o f 18-30 Mg ha −1 y −1 of dry matter (DM) [6,21,31,32]. The dry matter yield (DMY) of tubers can reach 7-17 Mg ha −1 y −1 [15, 19, 29, [32] [33] [34] [35] [36] [37] , and the DMY of aerial biomass (stems, leaves, inflorescences) can be as high as 31-35 Mg DM ha −1 y −1 [38] . Jerusalem artichoke is highly competitive against segetal vegetation, and it is resistant to pests and diseases. The species is also highly tolerant to drought and soil salinity, and it has low fertilizer requirements [20, [27] [28] [29] 39, 40, 41] . When grown as a perennial crop, JA is characterized by low production costs (energy inputs) because tubers can be left in soil for several years [6] . For these reasons, JA can be grown in marginal soils, and it does compete with food crops that are generally cultivated in fertile soils [21, 42] . Jerusalem artichoke can be effectively grown in low-input production technologies characterized by low consumption of agricultural materials [6, 44] . Due to its high resistance to biotic and abiotic stressors as well as high DMY, JA is a promising candidate for renewable energy production [15, [45] [46] [47] . Both aboveground plants parts (stems, leaves, inflorescences) and underground plant parts (tubers) can be converted to bio-based products in biorefineries [6, 23, 48, 49] . Due to a high content of carbohydrates (mainly inulin), JA tubers can be a rich source of substrate for the production of biogas and bioethanol [1, 6, 13, 18, 46, 50] , as well as 2, 3-butanediol, lactic acid, acetone-butanol, sorbitol and butyric acid [13] . Depending on the chemical composition of lignocellulose, aerial plant parts can be converted to solid fuel [47, 51] , transport biofuel [52] and bioproducts such as rubisco protein, flavonoids, organic acid, coumarins, antioxidants, polyacetylenes and sesquiterpene lactone [11, 13, 23, [52] [53] [54] . The energy gain of JA biomass ranges from 52-267 GJ ha −1 (aerial biomass) to 390 GJ ha −1 (tubers and aerial biomass) [47] . Jerusalem artichoke yields per unit area are determined by the applied production technology, mostly mineral fertilization [15, 19, 29, 36, 55, 56] . However, the production of mineral fertilizers is a highly energy-intensive process, which compromises the energy balance of agricultural crops and generates environmental problems [57] . Sewage sludge is a nutrient-J o u r n a l P r e -p r o o f rich fertilizer that offers an environmentally-friendly alternative to mineral fertilizers and contributes to reducing energy consumption in the production process [17, [58] [59] [60] . Sewage sludge is a by-product of wastewater treatment, and it is in plentiful supply due to rapid population growth and industrialization [61, 62] . According to estimates, sewage sludge production reached 60 million Mg in China alone [63,64], 50 million Mg in the European Union, and 40 million Mg in the USA [65,66] in 2020. Approximately 1 million Mg of sewage sludge was produced in Poland in 2019, including around 44,000 Mg in north-east Poland (voivodeships of Warmia and Mazury, and Podlasie) [67]. Sludge management poses a considerable environmental and economic problem around the world [61], and it is responsible for 30-50% of the total operating costs of municipal wastewater treatment [68-70]. One of the strategies for sewage sludge management is its agricultural use. Sewage sludge is abundant in organic matter, macronutrients and micronutrients, and it can be effectively used as fertilizer [70, [71] [72] [73] [74] , in particular in the production of energy (non-food) crops [58, 60] . Agricultural applications of sewage sludge deliver not only economic benefits, but they also contribute to environmental sustainability by retaining nutrients in local ecosystems [75] . In north-eastern Poland, around 38% of sewage sludge is used in agriculture [67] . Research has shown that the fertilization of energy crops with sewage sludge enhances biomass growth [57, 58, 76, 77] and increases the energy efficiency of crop production technologies [60]. The effects of sewage sludge fertilization on the energy efficiency ratio of JA biomass production have been sporadically investigated to date, and the present study aims to fill in this knowledge gap. The aim of this three-year experiment was to determine the influence of municipal sewage sludge on the yield of aerial biomass (fresh matter yield and dry matter yield) and the energy balance (energy inputs, energy output, energy gain and the energy efficiency ratio) of JA grown in a large-area farm in north-eastern (NE) Poland. J o u r n a l P r e -p r o o f 2. Materials and Methods 2.1. Field experiment A field experiment involving JA was conducted in 2018-2020 in the Agricultural Experiment Station in Bałcyny (53°35'50.0"N 19°50'27.3"E, NE Poland) operated by the University of Warmia and Mazury in Olsztyn. The experiment investigated the effects of two nitrogen fertilizer rates and types on the yield and energy potential of the aerial biomass of JA. The following treatments were established: (i) unfertilized control; (ii) 100 kg N ha −1 as sewage sludge; (iii) 100 kg N ha −1 as mineral fertilizer (34% ammonium nitrate); (iv) 160 kg N ha −1 as sewage sludge; (v) 160 kg N ha −1 as mineral fertilizer (34% ammonium nitrate). Sewage sludge rates (ii, iv) were determined in each year of the experiment based on the total nitrogen content of sludge (Table 1) . Sewage sludge was obtained from the wastewater treatment plant operated by the Water and Sewerage Company in Ostróda (NE Poland). The analyzed sewage sludge had a pH of 7.6-7.8 and the following composition: 124-147 g DM kg −1 , 614-724 g organic matter kg −1 DM, 57.4-59.7 g N kg −1 DM, 30.8-34.0 g P kg −1 DM, 41.6-47.9 g Ca kg −1 DM, 2.8-2.9 g Mg kg −1 DM, 0.26-0.79 mg Cd kg −1 DM, 359-412 mg Cu kg −1 DM, 25.8-35.4 mg Ni kg −1 DM, 12.8-18.0 mg Pb kg −1 DM, 775-1030 mg Zn kg −1 DM, 0.18-0.30 mg Hg kg −1 DM, and 58.5-67.8 mg Cr kg −1 DM. The presence of Salmonella spp., Ascaris spp., Trichuris spp. and Toxocara spp. DNA was not detected. The composition of sewage sludge was determined in the Environmental, Health and Safety Laboratory of SGS Poland Ltd. in Pszczyna. Enriched superphosphate (70 kg P2O5 ha −1 , 40% P2O5) and 150 kg of potash salt (150 kg K2O ha −1 , 50% K2O) were additionally applied in treatments with mineral nitrogen fertilization. Mineral fertilizer and sewage sludge were applied before tuber planting in the year of plantation establishment, and before the spring growing season in successive years. J o u r n a l P r e -p r o o f (Table 4) . Energy inputs were defined as the total consumption of energy associated with labor, fuel, tractors and farming machines, and agricultural materials. Energy inputs were divided into categories based on the respective energy fluxes: labor, fuel, farming machines and equipment, materials and farming operations (tillage, planting, fertilization, etc.). Biomass processing J o u r n a l P r e -p r o o f J o u r n a l P r e -p r o o f Highlights  Replacing mineral fertilizers with sewage sludge reduced energy input by 27-54%  Sewage sludge and mineral fertilizer delivered similar yield-forming effects  Regardless of fertilizer type, energy output peaked in response to 100 kg N ha −1  The energy efficiency ratio was twice higher after application of sewage sludge J o u r n a l P r e -p r o o f
doi:10.1016/ fatcat:xby2vy6jxfczddrjzsxqxa6ba4