Biyokütle külü ile zenginleştirilmiş arıtma çamuru kompostunda mikro-makro element ve ağır metal spesifikasyonunun incelenmesi = Investigation of heavy metal and micro-macro element speciation in biomass ash enriched sewage sludge compost

Abstract

ÖZET Bu çalışmanın amacı, arıtma çamuru kompostunu, besin içeriğini bitki mikro besin elementleri (Fe, Al, Cu, Ni, Zn, Na, Mn), makro besin elementler (P, K, Mg, Ca) açısından zengin biyokütle kül katkı maddelesi ile iyileştirmek ve arıtma çamurunun kompostlanması sırasında ağır metalleri (Cr, Cd, Pb) pasifleştirmektir. Özellikle arıtma çamurunun yüksek konsantrasyonlarda içerdikleri mikro-makro besin elementlerinin spesifikasyonlarının ortaya konması, ağır metal spesifikasyonunun belirlenmesi, bu atıklardan oluşturulan kompost ürünlerinin de bitki verim kalitesi ve çevresel risk açısından risk teşkil edip etmediğinin ortaya konmasında önemli bir noktadır. Çalışmamızda element türlerini belirlemek için sıralı ekstraksiyon yöntemi kullanılmıştır. Ülkeminzde arıtma çamurları yüksek organik madde miktarlarına rağmen düzenli depolama sahalarına atık sınıfında gönderilir ya da arazi dolgusu olarak değerlendirilirler. Bu çalışmada kanatlı hayvan çiftliklerinde oluşan organik atıkların yakılmasıyla oluşturulan biyokütle külünün belli oranlarda arıtma çamuru ve yardımcı malzeme olan ağaç talaşı ile kompostlanması yapılmıştır. Sonuçta, bu çalışmadan elde edilecek veriler, bu organik atıkların faydalı bir kullanım alanını da ortaya koyacaktır. Özellikle biyokütle külünün faydalarını hesaba katan kompost ilave endekslerinin oluşturulması, bu faaliyetin ileride ticari kullanımını arttırmaya da yardımcı olacaktır. Bu sayede hem düşük maliyetli hem de bölgedeki birçok üreticiyi kapsayarak atıkların büyük oranda azaltılması da sağlanacaktır. Sürdürülebilir üretim ve çevre çerçevesinde, organik atıklar için bilinçsizce uygulanan bertaraflar ortadan kaldırılacak ve meydana gelebilecek çevresel riskler önlenebilecektir. Malzemelerin karışım oranları, 2018 yılı Gıda, Tarım ve Hayvancılık Bakanlığı tarafından hazırlanan Tarımda Kullanılan Organik, Mineral ve Mikrobiyal Kaynaklı Gübrelere Dair Yönetmelik'te yer alan %7 NPK sınır şartına göre kuru ağırlıkta oluşturulmuştur. Bu sınır değere göre hesaplanan biyokütle kül miktarı, arıtma çamuru + odun talaşı karışımına (hacimce, 1:1) homojen olarak ilave edilerek kompost numunelerindeki nihai NPK içeriği kuru maddede; T0: %0, T1: %3,5, T2: %7,0 ve T3: %14,0 olarak belirlenmiş, kompostlar 45 gün boyunca takip edilmiştir. Elde edilen sonuçlarda Cr, Cd ve Pb, biyokütle külünün eklendiği tüm uygulamalarda inoksitlerle bileşik yapmış (mineral kısma bağlanmış, çökelmiş) ve çözünemeyen (kalıntı) formlar birincil fraksiyonlar olmuş, biyoyararlanım faktörü (BF) kül ilaveli gruplarda (<1% BF–Cr, 21% BF–Cd and 9% BF–Pb), kontrol grubuna oranla (46% BF–Cr, 47% BF–Cd ve 80% BF–Pb) daha düşük oranlarda ölçülmüştür. Biyokütle külü miktarı arttıkça (T1-T3), kalıntı Cr (%10-65), değiştirilebilir Cd ve organik olarak bağlı Cd sırası ile (%14 ve %21) ve inoksitlerle birleşik yapmış-Pb (%20-61) oranları artmıştır. Tüm kompostlarda, Fe, Al ve Cu'ın, organik bağlı ve inoksitlerle birleşik yapmış fraksiyonları birincil fraksiyon olmuştur. Kül ilavesi Mn ve Mg dışındaki tüm elementlerin biyoyararlanımını kontrol grubuna oranla azaltmıştır. Toplam Mn ve Mg'un %50'den fazlası, esas olarak değişebilir fraksiyonlarda yoğunlaşmıştır, bu da yüksek hareketlilik ve buna bağlı biyoyararlanım olduğunu göstermektedir (%42 BF–Mn ve %98 BF–Mg). Ni, Zn ve Na, İnoksitlerle bileşik oluşturmuş, organik bağlı ve kalıntı fraksiyonlarda bulunma eğilimindeyken, K ve P, değiştirilebilir ve organik bağlı fraksiyonlarda yoğunlaşmıştır. Bu çalışma, biyokütle külü ile zenginleştirilmiş arıtma çamuru kompstunun, ağır metalleri pasifleştirdiği ve zengin besin element içeriği ile biyoyararlanımlığının yüksek olması sebebi ile toprak ıslahında tercih edilmesi gereken en iyi strateji ve tekni olduğunu göstermektedir.

SUMMARY The objective of this study was to enrich the nutrient content of compost and to investigate the passivation and solubilization of plant micronutrients (Fe, Al, Cu, Ni, Zn, Na, Mn), macroelements (P, K, Mg, Ca), and heavy metals (Cr, Cd, Pb) during sewage sludge composting with nutrient-rich biomass ash additives. It is an important point to reveal the specifications of micro-macro nutrients that the sewage sludge contains in high concentrations, to determine the heavy metal specification, and to reveal whether the compost products formed from these wastes pose a risk in terms of plant yield quality and environmental risk. In our study, sequential extraction method was used to determine the element types. Despite the high organic matter content of sewage sludge in our country, they can be obtained as landfill or sent to landfills as waste. In this study, composting of biomass ash, which is created by burning organic wastes in poultry farms, was made with treatment sludge and wood sawdust as auxiliary material in certain proportions. As a result of our study, a beneficial and environmental disposal method will be revealed for both treatment sludge and biomass ash. Establishing compost addition indices that specifically take into account the benefits of biomass ash will also help to increase the commercial use of this activity in the future. Treatment sludge was obtained from Sakarya Metropolitan Municipality Karaman Wastewater Treatment Plant. The physico-chemical analysis results of the treatment sludge used in the study were obtained as follows: pH 6.83, EC 2160 μS cm-1, organic matter content 57%, total N 2.316%, P 710 mg kg-1, K 5120 mg kg-1. Micro-macro element and heavy metal content, respectively, micro elements; Fe 18485 mg kg-1, Cu 78 mg kg-1, Mn 468 mg kg-1, Zn 327 mg kg-1, Ni 28 mg kg-1, Al 18106 mg kg-1, Na 819 mg kg-1, macro elements; Mg 6850 mg kg-1, Ca 51075 mg kg-1, Si 737 mg kg-1 and heavy metals; Cr 173 mg kg-1, Cd 1.08 mg kg-1, Pb 36.7 mg kg-1, Ba 815 mg kg-1, Hg 0.912 mg kg-1. It has been observed that the sewage sludge is rich in organic matter, nitrogen, phosphorus, potassium, micro-macro nutrients required for plant growth. Sewage sludge has been preferred as an organic nutrient provider in compost mixtures. Biomass ash was obtained from a biomass power plant located in Sakarya. This facility burns 500-550 tons of organic waste per day. Approximately 80% of this mixture consists of poultry organic waste. While the biomass ash coming out of the facility is a difficult waste to deal with for other disposal methods due to its high nitrogen content, when mixed into the treatment sludge for composting, it turns into an ideal nitrogen, i.e. nutrient source for microbiological activities, and the excess nitrogen is converted into forms that can be tolerated by composting and taken up for the plant. Composition of biomass ash obtained as follows: 839 mg kg -1 B, 20179 mg kg -1 Na, 33390 mg kg -1 Mg, 26640 mg kg -1 Al, 100558 mg kg -1 K, 171116 mg kg -1 Ca, 2143 mg kg -1 Ti, 119.8 mg kg -1 Cr, 2948 mg kg -1 Mn, 26042 mg kg -1 Fe, 100.1 mg kg -1 Co, 267.3 mg kg -1 Cu, 1222 mg kg -1 Zn, 236.2 mg kg -1 Sr, 507.6 mg kg -1 Ba, 72 mg kg -1 Ni, 3.92 mg kg -1 Pb, 1.4 mg kg -1 Cd, 97642 mg kg -1 p. The composting process was carried out in aerated (aerobic) rectangular plastic boxes with a volume of 5 L. The mixing ratios of the materials have been established in dry weight according to the 7% NPK limit requirement in the Regulation on Organic, Mineral and Microbial Originated Fertilizers Used in Agriculture prepared by the Ministry of Food, Agriculture and Livestock in 2018. The amount of biomass ash calculated according to this limit value was added homogeneously to the treatment sludge + wood sawdust mixture (by volume, 1:1) and the final NPK content in the compost samples was determined in the dry matter; T0: 0%, T1: 3.5%, T2: 7.0%, and T3: 14.0% dry weight (DW), weight/weight (w/w) biomass ash was added to the sewage sludge+sawdust mixture (volume, 1:1) to obtain the final NPK content and monitored over a 45-day period. Sawdust was used as auxiliary material. The sequential extraction method was used to determine the elemental species. Mixed pile compost method was used in the study. Unlike passive composting, this method is based on regular mixing so that microorganisms can get enough oxygen and remove moisture. For this reason, measurements of the daily compost were taken every day during the follow-up process, then each sample was mixed and aerated. Gas formation (CH4, CO2, O2, H2S) in manually mixed composts for 45 days was monitored with a Geotech GA5000 Portable gas analyzer to remove volatile and other toxic substances and to ensure good aeration and homogeneity. In addition, microbial activity was monitored daily by measuring the temperature with a digital thermometer receiver at different locations (upper, middle and lower layers) in the compost. Determination of total heavy metal content alone does not provide sufficient information about bioavailability risks, remobilization (remobilization) and behavior of heavy metals in the environment. For this reason, we need to know in which forms and how much heavy metals dissolve. To determine the micro-macro element and heavy metal specification, samples were taken at day 0 (week 1), day 9 (week 2), day 18 (week 3), day 27 (week 4), day 36 (week 5) and day 45 (week 6) were analyzed. To ensure representative sampling, samples were taken from three different positions in the reactors and homogenized. The resulting samples (5 g) were oven dried (70 °C) and ground to pass through a 2 mm sieve for further analysis. Micro (Fe, Al, Cu, Ni, Zn, Na, Mn) - macro (P, K, Mg, Ca) element and heavy metal (Cr, Cd, Pb) specification small to Sposito procedure (Sposito et al., 1982) With a change (Agbenin and Atin; 2003) method, it was applied as four steps, except for the total element concentration treated in acid, which allows the detection of elements in the form of residues. These four steps can be briefly summarized as follows. (1) Water soluble (free ionic form) (mobilized); 5 g of air dry and sieved sample was put into the centrifuge tube without weighing. 25 ml of distilled water was added to it. It was shaken for 2 hours in a shaker and separated by centrifugation at 3500 rpm for 10 minutes and filtered through Whatmann 42 filter paper into a 100 ml bottle. The filtrate was sent to the instrument for element determination. The centrifuge tube was weighed and the second step was taken. (2) Exchangeable (K2SO4) (mobilized); 25 ml of 0.25 M K2SO4 solution was added to the centrifuge tube and sample at hand and shaken in a shaker for 16 hours and separated by centrifugation at 3500 rpm for 10 minutes and filtered through Whatmann 42 filter paper into a 100 ml bottle. The filtrate was sent to the instrument for heavy metal determination. The centrifuge tube was weighed and the third step was taken. (3) Organic bound (NaOH) (mobilizable); 25 ml of 0.5 M NaOH solution was added to the centrifuge tube and sample at hand and shaken in a shaker for 16 hours and separated by centrifugation at 3500 rpm for 10 minutes and filtered through Whatmann 42 filter paper into a 100 ml bottle. The filtrate was sent to the instrument for heavy metal determination. The centrifuge tube was weighed and the fourth step was taken. (4) Conjugated with Inoxides (EDTA) (bound to mineral fraction, precipitated) (mobilizable); 25 ml of 0.5 M EDTA solution was added to the centrifuge tube and sample at hand and shaken in a shaker for 6 hours and separated by centrifugation at 3500 rpm for 10 minutes and filtered through Whatmann 42 filter paper into a 100 ml bottle. The filtrate was sent to the instrument for heavy metal determination. (5) Residual (Calculated by subtracting the results obtained from the above-mentioned steps from the total elemental concentration) (Total elemental concentration is calculated by adding 6 ml of HNO3 (65%), 1 ml of H2O2 (30%) to 250 mg of sample in a microwave oven (Sorisole). -Bg, Italy) It was measured by burning for 10 minutes at 170 °C, 15 minutes at 200 °C, 10 minutes at 100 °C and 10 minutes at 100 °C for a total of 45 minutes and after cooling the samples, it was made up to 25 ml with ultrapure water.) The bioavailability factor (BF) was calculated by taking the ratio of the metal content in the water-soluble and exchangeable fractions (1 and 2) to the total metal content. Cr, Cd and Pb showed higher affinity to the residual fraction and occluded in the oxide fraction, which decreased the bioavailability factor (BF) (<1% BF-Cr, 21% BF-Cd and 9% BF-Pb) compared to the control treatment (46% BF-Cr, 47% BF-Cd and 80% BF-Pb). As the amount of biomass ash increased (T1- T3), the percentages of residual Cr (Res-Cr) (10-65%), exchangeable Cd (Exc-Cd) and organically bound Cd (Org-Cd) (14% and 21%), and oxides-Pb (Oxi-Pb) (20-61%) increased. In all composts, Fe, Al, and Cu were associated with organically bound and oxides-entrapped fractions. More than 50% of total Mn and Mg were concentrated mainly in exchangeable fractions, suggesting high mobility and bioavailability (42% BF-Mn and 98% BF-Mg). Ni, Zn, and Na tended to be present in oxide-bound, organically bound, and residual fractions, while K and P were associated with exchangeable and organically bound fractions. The composting process tends to passivate heavy metals because it accelerates organic matter humidification and changes chemical parameters. In the data obtained in this study, besides the addition of biomass ash to the compost, it has been shown that during composting, organic matter mineralization and heavy metal release, heavy metal dissolution by decreasing pH, metal biosorption by microbial biomass, and humic substances formed during composting, respectively. showed the formation of metal complexes with. In the physical examinations made during and at the end of composting, it was observed that the compost structure of T0 (control) application was unstable and muddy compared to other applications (T1, T2, T3). A more stable compost structure was observed in the applications with biomass ash addition, T1, T2 and T3, and it was observed that the T3 application during mixing was more earthy and stable than the other applications (T1, T2). This is an indication that biomass ash enriches the compost, promotes the composting process and has a healing effect in composting. If the compost created in this way is used as fertilizer and recycled as an economic product, it will be revealed whether these elements are in a form that can be taken for the plant. In this way, it will be ensured that wastes are reduced to a large extent by covering many producers in the region and with a low cost. In the framework of sustainable production and environment, unconscious disposal of organic wastes will be eliminated and environmental risks that may occur will be prevented. In the general evaluation made as a result of the study, the addition of biomass ash to the sewage sludge compost decreased the bioavailability of all elements except Mn and Mg. Mg and Mn showed greater affinity for their Exchangeable and water-soluble fractions, while the remaining other micro-macro elements and heavy metals were mostly in the organic bound and compounding fractions with Inoxides. BF analyzes proved that heavy metals were not in a suitable form for plant uptake. A large proportion of the fractions more resistant to extraction ( residual form) showed that the heavy metals were in more stable forms. The overall results suggest that composting sewage sludge with biomass ash may be the best strategy and technique to overcome soil application bottlenecks because it passivates heavy metals and improves the bioavailability of plant nutrients.