Contact/s:
Elena Bortolazzo
e.bortolazzo@crpa.it
Arianna Pignagnoli
Solid-liquid Separation to Optimize Livestock Effluent Management and Reduce Environmental Impact
Italy
Italy, continental
1. Livestock effluents,
2. Solid-liquid separation,
3. Nutrient management
Thematic Areas
Production System/s
Summary for Practicioners on the Main Finding(s)/Innovative solution(s)
Livestock effluents management poses environmental challenges, linked to ammonia and greenhouse gas emissions, as well as logistical ones due to the large volumes to be stored and spread.
A practical and advantageous solution for farms is solid-liquid separation, a mechanical treatment that divides the slurry into two distinct and more easily manageable matrices.
This technique produces a clarified liquid fraction and a solid fraction. The liquid fraction, rich in readily available ammoniacal nitrogen, facilitates mixing in the tanks by reducing the formation of surface crusts, lowers odor and greenhouse gas emissions, and is ideal for fertigation and in-house recycling.
The solid fraction concentrates slow-release organic nitrogen and phosphorus, making it an excellent soil conditioner that can replace manure.
The separation systems that can be adopted on farms vary and allow for the separation of coarse solids only, meaning those larger than 0.1 mm (vibrating or rotary screens, screw press and counter-rotating roller separators), or the separation of both coarse and fine solids, meaning those smaller than 0.1 mm (settling tanks, flotation units, centrifuges).
The most widespread separators, offering the best compromise between costs and management efficiency, are counter-rotating rollers or screw presses, whereas centrifuges offer higher yields but require significantly larger investments.
Summary for Practicioners in Native Language
La gestione degli effluenti zootecnici pone sfide ambientali, legate alle emissioni di ammoniaca e di gas serra, e logistiche a causa dei grandi volumi da stoccare e spandere. Una soluzione pratica e vantaggiosa per le aziende agricole è la separazione solido-liquida, un trattamento meccanico che divide il liquame in due matrici distinte e più facilmente gestibili.
Questa tecnica produce una frazione liquida chiarificata e una frazione solida. La frazione liquida, ricca di azoto ammoniacale a pronto effetto, facilita la miscelazione nelle vasche riducendo la formazione di croste superficiali, abbassa le emissioni odorigene e di gas serra, ed è ideale per l’uso fertirriguo e per il riciclo in stalla.
La frazione solida concentra azoto organico a lento rilascio e fosforo, prestandosi come ottimo ammendante sostitutivo del letame.
I sistemi di separazione adottabili in allevamento sono vari e permettono di ottenere la sola separazione dei solidi grossolani, cioè di quelli con dimensioni maggiori di 0,1 mm (vagli vibranti o rotativi, separatori a compressione elicoidale e a rulli contrapposti), oppure la separazione deisolidi grossolani assieme a quelli fini, cioè quelli di dimensioni inferiori a 0,1 mm (sedimentatori, flottatori, centrifughe).
I separatori più diffusi, che offrono il miglior compromesso tra costi ed efficienza di gestione, sono quelli a rulli contrapposti o a compressione elicoidale, mentre le centrifughe offrono rese superiori ma richiedono investimenti notevolmente maggiori.
Additional Information
Solid-liquid separation is highly recommended as a strategic investment for farms with storage capacities exceeding 500 cubic meters, scattered fields, or locations within Nitrate Vulnerable Zones, as it allows for the cost-effective export of nutrients to unrestricted areas.
However, this technique is not economically justified for small-scale operations with less than 50 tons of live weight or for those that spread effluents exclusively within a 3-5 km radius from the farm center.
Furthermore, while high-efficiency systems like centrifuges offer superior yields, they involve significant investment and operational costs, sometimes requiring expensive chemical additives such as polyelectrolytes to increase separation efficiency. To maximize the benefits and ensure proper equipment sizing, it is crucial to analyze livestock effluent samples and consult technical experts before making an investment; for instance, counter-rotating rollers are optimal for straw-rich cattle manure, whereas screw presses provide excellent operational flexibility for effluents with a dry matter content above 2%.