Remediasi Kualtas Air Danau Eks Tambang Pasir untuk Kegiatan Perikanan

Abstract

Kegiatan pertambangan pasir berskala besar sering kali berdampak buruk terhadap kondisi lingkungan dan ekosistem. Berbagai penelitian menunjukkan bahwa besi (Fe) sering ditemui pada lokasi pertambangan. Besi (Fe) dan dan sulfur (S) adalah indikator pada daerah pertambangan yang biasanya menghasilkan senyawa asam berbasis Fe. Unsur kimia makro pada mineral pasir mengandung unsur Fe yang lebih dominan yang dapat mencapai 30% dari semua unsur penyusunnya. Salah satu wilayah yang memiliki potensi pertambangan pasir sangat besar adalah Kecamatan Pasir Sakti, Kabupaten Lampung Timur, Provinsi Lampung. Luas keseluruhan danau-danau eks galian pasir diperkirakan mencapai 1000 ha. Kondisi danau-danau di lahan eks tambang pasir di Kecamatan Pasir Sakti, saat ini tidak termanfaatkan. Lahan eks tambang pasir dengan karakteristik yang spesifik dan tidak optimal, pada dasarnya merupakan lahan yang potensial untuk kegiatan pemeliharaan ikan, namun kondisinya belum ideal. Kualitas air yang tidak optimum, bersifat asam, dan kandungan logam berat menjadikan pemanfaatannya membutuhkan perlakuan khusus. Salah satu perlakuan yang dapat diterapkan adalah fitoremediasi untuk memperbaiki kualitas air agar sesuai untuk kegiatan pemeliharaan ikan. Penelitian ini bertujuan: 1) Menggali informasi tentang kualitas air (fisika, kimia, dan biologis/fitoplankton) pada danau-danau eks galian pasir. 2) Menganalisis kesesuaian perairan eks galian pasir untuk kegiatan pemeliharaan ikan. 3) Menguji efektivitas tumbuhan air untuk mereduksi konsentrasi Fe pada air dari danau-danau eks galian pasir agar layak untuk kegiatan pemeliharaan ikan, dan 4) Menguji coba kombinasi fotoremediasi menggunakan tumbuhan air dan adsorban (biochar dan jerami padi) untuk mempercepat reduksi Fe dalam air. Hasil penelitian diharapkan dapat bermanfaat bagi pengelolaan dan pemanfaatan lahan eks galian pasir di Kecamatan Pasir Sakti Lampung Timur, agar bermanfaat bagi masyarakat. Pengamatan kualitas fisika, kimia dan biologi perairan dilakukan pada bulan Januari-Desember 2019, di tiga stasiun yang berbeda. Pengukuran kualitas air meliputi kedalaman, suhu, kecerahan, total suspended solid (TSS), total disolved solid (TDS), pH, konsentrasi oksigen terlarut, fosfat (PO4), nitrit (NO2), nitrat (NO3), konsentrasi Fe, dan sulfat (SO4), serta keanekaragaman fitoplankton. Tingkat kesesuaian perairan untuk pemeliharaan ikan dihitung dengan metode matching and scoring. Percobaan fitoremediasi dilakukan pada kolam semi outdoor menggunakan tumbuhan air Azolla pinnata, Eichhornia crassipes, dan Salvinia molesta dengan luas tutupan yang berbeda. Pengukuran konsentrasi Fe dalam air, serta pada akar dan daun tumbuhan air dilakukan secara periodik dari awal hingga akhir penelitian, menggunakan inductively coupled plasma-atomic emission spectrometry (ICP-AES). Efektivitas reduksi Fe diukur dengan menghitung nilai removal efficiency. Bioconcentration factors (BCF) dihitung untuk menduga kemampuan tumbuhan dalam menghilangkan senyawa logam dari tanah/air/substrat. Translocation factors (TF) dihitung untuk menggambarkan kemampuan tumbuhan air mentransfer logam dari akar ke batang dan daun. Perlakuan fitoremediasi lanjutan dilakukan dengan kombinasi tumbuhan uji dan arang kayu (biochar) serta jerami padi agar reduksi Fe dapat berlangsung cepat. Pengamatan struktur mikro jaringan tumbuhan uji dilakukan menggunakan scanning electron microscopy (SEM) yang terintegrasi dengan energy dispersive X-ray spectroscopy (EDX). Berdasarkan pengamatan keragaman jenis fitoplankton di danau-danau eks tambang pasir, ditemukan 47 jenis yang terbagi dalam 5 kelas, yaitu Chlorophyceae (23 jenis), Bacillariophyceae (12 jenis), Cyanophyceae (7 jenis), Euglenophyceae (3 jenis), dan Chrysophyceae (2 jenis). Kepadatan rata-rata fitoplankton terendah ditemukan pada bulan Juni (12.297 sel/L), dan tertinggi pada bulan Desember (51.795 sel/L). Indeks keanekaragaman berkisar antara 1,370–2,091. Berdasarkan kepadatan fitoplankton, danau-danau eks galian pasir di Kecamatan Pasir Sakti termasuk dalam kategori oligotrophic. Konsentrasi Fe pada danau-danau eks galian pasir berkisar antara 0,159–5,898 mg/L, jauh di atas nilai yang disarankan untuk kegiatan pemeliharaan ikan (0,02 mg/L). Analisis kesesuaian lahan eks galian pasir untuk kegiatan pemeliharaan ikan sebesar 64%-68% yang termasuk kelas S3 atau sedikit sesuai (marginally suitable). Rendahnya nilai kesesuaian lahan dipengaruhi oleh kecerahan, O2 terlarut, suhu, pH, amonia, fosfat, dan besi, sedangkan salinitas, nitrat, sulfat, dan kepadatan fitoplankton tergolong layak untuk kegiatan pemeliharaan ikan. Penurunan konsentrasi Fe tertinggi diperoleh pada perlakuan fitoremediasi menggunakan tumbuhan air A. pinnata (luas tutupan 75%); diikuti perlakuan E. crassipes (luas tutupan 50%), dan perlakuan S. molesta (luas tutupan 50%), dengan nilai removal efficiency berturut-turut sebesar 98,12%; 97,60% dan 97,29%. Konsentrasi Fe yang layak untuk pemeliharaan ikan dicapai setelah 21 hari perlakuan. Berdasarkan nilai BCF dan TF, seluruh tumbuhan uji terbukti efektif untuk mereduksi Fe. Kombinasi antara tumbuhan air dan penambahan biochar juga terbukti efektif untuk mempercepat reduksi Fe, dengan nilai removal efisiensi 97,56%–98,18%. Konsentrasi Fe yang layak untuk pemeliharaan ikan dicapai pada hari ke-9 untuk tanaman E. crassipes dan hari ke-12 untuk A. pinnata dan S. molesta. Sebaliknya, penambahan jerami padi tidak terbukti efektif mempercepat reduksi Fe dalam air, karena jerami padi membusuk sehingga konsentrasi Fe yang telah terserap terlepas kembali ke air. Pengamatan SEM-EDX menunjukkan telah terjadi perubahan struktur mikro jaringan tumbuhan air pada awal dan akhir perlakuan, akibat adanya deposit mineral logam Fe pada jaringan tumbuhan air dan pada biochar. Jaringan jerami padi mengalami pembusukan. Penelitian ini membuktikan bahwa tumbuhan air A. pinnata, E. crassipes, dan S. molesta terbukti efektif dan dapat diandalkan untuk mereduksi Fe pada air di lahan eks galian pasir. Reduksi Fe dengan perlakuan A. pinnata dengan luas tutupan 75%, E. crassipes dengan luas tutupan 50%, dan S. molesta dengan luas tutupan 50% disarankan dapat diaplikasikan untuk mereduksi konsentrasi Fe selama 21 hari perlakuan. Penambahan biochar/arang kayu, terbukti berhasil mempercepat reduksi Fe dari 21 hari menjadi 9–12 hari. Sebaliknya, penambahan jerami padi tidak terbukti efektif untuk mempercepat proses fitoremediasi Fe. Penerapan fitoremediasi dengan tumbuhan air A. pinnata, E. crassipes, dan S. molesta dengan luas tutupan 50% dikombinasikan dengan biochar/aramg kayu dengan ketebalan 5 cm selama 9–12 hari dapat diaplikasikan sebelum air dimanfaatkan untuk kegiatan pemeliharaan ikan. Hasil penelitian ini memberikan harapan bagi upaya pemanfaatan air dari danau-danau eks galian pasir di Kecamatan Pasir Sakti, untuk dapat dimanfaatkan bagi kegiatan pemeliharaan ikan.

Large-scale sand mining activities often have a negative impact on environments and ecosystems. Various studies have shown that iron (Fe) is often found in ex-sand mining sites. Iron (Fe) and sulfur (S) are metal and acids indicator in mining areas which usually produce iron-based acid compounds. The macro chemical elements in sand minerals contain Fe which is more dominant which can reach 30% of all its constituent elements. One area that has a very large potential sand mining sites is Pasir Sakti District, East Lampung Regency, Lampung Province. The total area of the ex-sand pit lakes is estimated at 1,000 ha. The condition of the ex-san pit lakes in the sand mining area in Pasir Sakti District is currently not being utilized. Ex-sand pit lakes with specific and non-optimal characteristics is basically a potential but not ideal for aquaculture. The water quality is not optimum, acidic, and contains heavy metals, so its utilization requires special treatment. One of the treatments that can be applied is phytoremediation to improve water quality to make it suitable for fish culture. This study aims to: 1) Obtain information on water quality (physics, chemistry, and biology/phytoplankton) of ex-sand pit lakes. 2) Assessing the suitability of water quality of ex-sand pit lakes for fish culture. 3) Analyzing the effectiveness of aquatic plants to reduce Fe concentration in water from ex-sand pit lakes to make it suitable for fish culture, and 4) Trials a combination of photoremediation using aquatic plants and adsorbents (biochar and rice straw) to accelerate reduction of Fe in water. The results of the study are expected to be useful for the management and use of ex-sand pit lakes in Pasir Sakti District, East Lampung, so that it is beneficial for the community. Observations of the physical, chemical and biological water qualities were carried out in January-December 2019, at three stations. Water quality measurements include depth, temperature, clarity, total suspended solid (TSS), total dissolved solid (TDS), pH, dissolved oxygen, phosphate (PO4), nitrite (NO2), nitrate (NO3), concentrations of Fe, concentrations of sulfate (SO4), as well as the diversity of phytoplankton. Suitability of the water quality for fish culture is calculated by the matching and scoring method. Phytoremediation experiments were carried out in semi-outdoor ponds treated use aquatic plants (Azolla pinnata, Eichhornia crassipes, and Salvinia molesta) with different cover areas. Measurement of Fe concentration in water, as well as in roots and leaves of aquatic plants was carried out periodically from the beginning to the end of the study, using inductively coupled plasma-atomic emission spectrometry (ICP-AES). The effectiveness of Fe reduction is measured by calculate the value of removal efficiency. Bio-concentration factors (BCF) were calculated to estimate the ability of plants to remove metal from soil/water/substrate. Translocation factors (TF) were calculated to describe the ability of aquatic plants to transfer metals from roots to stems and leaves. Further phytoremediation treatment was carried out by combining of aquatic plants and wood charcoal (biochar) and rice straw to accelerate Fe reduction. Observation of the microstructure of aquatic plant tissue was carried out using scanning electron microscopy (SEM) which is integrated with energy dispersive X-ray spectroscopy (EDX). Observations of phytoplankton diversity in ex-sand pit lakes have been carried out. Forty-seven species were found which were divided into 5 classes: Chlorophyceae (23 species), Bacillariophyceae (12 species), Cyanophyceae (7 species), Euglenophyceae (3 species) and Chrysophyceae (2 species). The lowest average density of phytoplankton was found in June (12,297 cell/L), and the highest in December (51,795 cell/L). The diversity index ranged from 1.370–2.091. Based on the density of phytoplankton, ex-sand pit lakes in Pasir Sakti District are included in the oligotrophic category. Fe concentrations in ex-sand pit lakes ranged from 0.159–5.898 mg/L, well above the recommended value for fish culture (0.02 mg/L). Analysis of the suitability of water quality ex-sand pit lakes for fish culture is 64%–68% (marginally suitable). The low suitability value is mainly influenced by clarity, dissolved oxygen, temperature, pH, ammonia, phosphate, and iron concentration, meanwhile, salinity, nitrate, sulfate, and phytoplankton density were considered suitable for fish culture. Phytoremediation treatments showed, the highest decrease in Fe concentration was obtained in the treatment using A. pinnata (75% coverage area); followed by E. crassipes treatment (50% cover area), and S. molesta treatment (50% coverage area), with removal efficiency of 98.12%; 97.60% and 97.29% respectively. TheFe concentration thet is feasible for fish culture was achieved after 21 days of treatment. Based on the values of BCF and TF, all of the aquatic plants proved to be effective in reducing Fe. The combination of treatment between aquatic plants and biochar was also proven to be effective in accelerating the reduction of Fe, with a removal efficiency value of 97.56%–98.18%. Adequate Fe concentration for fish culture was achieved on day 9 for E. crassipes and day 12 for A. pinnata and S. molesta. Otherwise, the addition of rice straw is not proven to be effective in accelerating the reduction of Fe in the water, because the rice straw undergoes decay so that the concentration of Fe that has been absorbed by the straw is released back into the water. SEM-EDX observations showed that there was a change in the microstructure of the aquatic plant tissue at the beginning and at the end of the treatment. This occurs due to the presence of Fe mineral deposits in aquatic plant tissues and in biochar. While the rice straw tissue is decaying. This study proved that the aquatic plants A. pinnata, E. crassipes, and S. molesta proved effective and reliable to reduce Fe in water in ex-sand pit lakes. Fe reduction with A. pinnata treatment with 75% coverage area, E. crassipes with 50% cover area, and S. molesta with 50% cover area are suggested to be applied to reduce Fe concentration for 21 days of treatment. This study proved that the aquatic plants A. pinnata, E. crassipes, and S. molesta proved effective and reliable to reduce Fe in water in ex-sand pit lakes. Fe reduction with A. pinnata treatment with 75% coverage area, E. crassipes with 50% cover area, and S. molesta with 50% cover area are suggested to be applied to reduce Fe for 21 days of treatment. The addition of biochar has proven successful in accelerating the reduction of Fe from 21 days to 9 -12 days. On the other hand, the addition of rice straw was not proven to be effective in accelerating the process of Fe reduction. The application of phytoremediation using A. pinnata, E. crassipes, and S. molesta with a cover area of 50% combined with biochar with a thickness of 5 cm for 9-12 days can be applied before the water is used for fish culture. The results of this study provide an opportunity for efforts to utilize water on ex-sand pit lakes in Pasir Sakti District, to be used for aquaculture by the community.